(Slip Opinion) OCTOBER TERM, 2009 1 

Syllabus 

NOTE: Where it is feasible, a syllabus (headnote) will be released, as is

being done in connection with this case, at the time the opinion is issued.

The syllabus constitutes no part of the opinion of the Court but has been

prepared by the Reporter of Decisions for the convenience of the reader. 

See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337. 

SUPREME COURT OF THE UNITED STATES 

Syllabus 

KRUPSKI v. COSTA CROCIERE S. P. A. 

CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR 

THE ELEVENTH CIRCUIT 

No. 09–337. Argued April 21, 2010—Decided June 7, 2010 

Petitioner Krupski sought compensation for injuries she suffered on a 

cruise ship. Her passenger ticket, which was issued by Costa Cruise

Lines, identified respondent Costa Crociere S. p. A. as the carrier; required an injured party to submit to the carrier or its agent written 

notice of a claim; required any lawsuit to be filed within one year of 

the injury; and designated a specific Federal District Court as the exclusive forum for lawsuits such as Krupski’s. The front of the ticket 

listed Costa Cruise’s Florida address and made references to “Costa 

Cruises.” After Krupski’s attorney notified Costa Cruise of her 

claims but did not reach a settlement, Krupski filed a diversity negligence action against Costa Cruise. Over the next several months— 

after the limitations period had expired—Costa Cruise brought Costa

Crociere’s existence to Krupski’s attention three times, including in 

its motion for summary judgment, in which it stated that Costa Crociere was the proper defendant. Krupski responded and moved to

amend her complaint to add Costa Crociere as a defendant. The District Court denied Costa Cruise’s summary judgment motion without

prejudice and granted Krupski leave to amend. After she served 

Costa Crociere with an amended complaint, the court dismissed 

Costa Cruise from the case. Thereafter, Costa Crociere—represented 

by the same counsel as Costa Cruise—moved to dismiss, contending 

that the amended complaint did not satisfy the requirements of Federal Rule of Civil Procedure 15(c), which governs when an amended 

pleading “relates back” to the date of a timely filed original pleading

and is thus timely even though it was filed outside an applicable limitations period. The Rule requires, inter alia, that within the Rule 

4(m) 120-day period for service after a complaint is filed, the newly

named defendant “knew or should have known that the action would 
2 KRUPSKI v. COSTA CROCIERE S. P. A. 

Syllabus 

have been brought against it, but for a mistake concerning the proper 

party’s identity.” Rule 15(c)(1)(C)(ii). The District Court found this 

condition fatal to Krupski’s attempt to relate back. It concluded that 

she had not made a mistake about the proper party’s identity because, although Costa Cruise had disclosed Costa Crociere’s role in 

several court filings, she nonetheless delayed for months filing an 

amended complaint. The Eleventh Circuit affirmed, finding that 

Krupski either knew or should have known of Costa Crociere’s identity as a potential party because she furnished the ticket identifying 

it to her counsel well before the limitations period ended. It was 

therefore appropriate to treat her as having chosen to sue one potential party over another. Additionally, the court held that relation

back was not appropriate because of Krupski’s undue delay in seeking to amend the complaint. 

Held: Relation back under Rule 15(c)(1)(C) depends on what the party 

to be added knew or should have known, not on the amending party’s 

knowledge or timeliness in seeking to amend the pleading. Pp. 7–18.

(a) The Rule’s text does not support the Eleventh Circuit’s decision 

to rely on the plaintiff’s knowledge in denying relation back. The 

question under Rule 15(c)(1)(C)(ii) is not whether Krupski knew or 

should have known Costa Crociere’s identity as the proper defendant,

but whether Costa Crociere knew or should have known during the

Rule 4(m) period that it would have been named as the defendant but

for an error. The plaintiff’s information is relevant only if it bears on

the defendant’s understanding of whether the plaintiff made a mistake regarding the proper party’s identity. It would be error to conflate knowledge of a party’s existence with the absence of mistake.

That a plaintiff knows of a party’s existence does not preclude her 

from making a mistake with respect to that party’s identity. Making

a deliberate choice to sue one party over another while understanding the factual and legal differences between the two parties may be

the antithesis of making a mistake, but that does not mean that any 

time a plaintiff is aware of the existence of two parties and chooses to

sue the wrong one, the proper defendant could reasonably believe

that the plaintiff made no mistake. A plaintiff might know that the

prospective defendant exists but nonetheless choose to sue a different 

defendant based on a misunderstanding about the proper party’s 

identity. That kind of deliberate but mistaken choice should not foreclose a finding that Rule 15(c)(1)(C)(ii) has been satisfied. This reading is consistent with relation back’s purpose of balancing the defendant’s interests protected by the statute of limitations with the

preference of the Federal Rules of Civil Procedure in general, and 

Rule 15 in particular, for resolving disputes on their merits. It is also 

consistent with the history of Rule 15(c)(1)(C). And it is not fore-
Cite as: 560 U. S. ____ (2010) 3 

Syllabus 

closed by Nelson v. Adams USA, Inc., 529 U. S. 460. Pp. 7–13.

(b) The Eleventh Circuit also erred in ruling that Krupski’s undue

delay in seeking to file, and in eventually filing, an amended complaint justified its denial of relation back under Rule 15(c)(1)(C). The 

Rule plainly sets forth an exclusive list of requirements for relation 

back, and the plaintiff’s diligence is not among them. Moreover, it 

mandates relation back once its requirements are satisfied; it does

not leave that decision to the district court’s equitable discretion. Its 

mandatory nature is particularly striking in contrast to the inquiry 

under Rule 15(a), which gives a district court discretion to decide

whether to grant a motion to amend a pleading before trial. See 

Foman v. Davis, 371 U. S. 178, 182. Rule 15(c)(1)(C) permits a court 

to examine a plaintiff’s conduct during the Rule 4(m) period, but only 

to the extent the plaintiff’s postfiling conduct informs the prospective

defendant’s understanding of whether the plaintiff initially made a

“mistake concerning the proper party’s identity.” The plaintiff’s postfiling conduct is otherwise immaterial to the relation-back question.

Pp. 13–15. 

(c) Under these principles, the courts below erred in denying relation back. Because the original complaint (of which Costa Crociere

had constructive notice) made clear that Krupski meant to sue the

company that “owned, operated, managed, supervised and controlled”

the ship on which she was injured and also indicated (mistakenly)

that Costa Cruise performed those roles, Costa Crociere should have

known that it avoided suit within the limitations period only because 

of Krupski’s misunderstanding about which “Costa” entity was in 

charge of the ship—clearly a “mistake concerning the proper party’s 

identity.” That Krupski may have known the ticket’s contents does 

not foreclose the possibility that she nonetheless misunderstood crucial facts regarding the two companies’ identities. Especially because 

the face of the complaint plainly indicated such a misunderstanding,

respondent’s contention that it was entitled to think she made no

mistake is not persuasive. Moreover, respondent has articulated no 

strategy that it could reasonably have thought Krupski was pursuing

in suing a defendant that was legally unable to provide relief. Nothing in Krupski’s conduct during the Rule 4(m) period suggests that 

she failed to name Costa Crociere because of anything other than a 

mistake. The interrelationship between Costa Cruise and Costa Crociere and their similar names heighten the expectation that Costa 

Crociere should suspect a mistake when Costa Cruise is named in a

complaint actually describing Costa Crociere’s activities. In addition, 

Costa Crociere’s own actions contributed to passenger confusion over

“the proper party”: The front of the ticket advertises that “Costa 

Cruises” has achieved a certification of quality without clarifying 
4 KRUPSKI v. COSTA CROCIERE S. P. A. 

Syllabus 

which “Costa” company is meant. And as shown in similar lawsuits, 

Costa Crociere is evidently well aware that the difference between it 

and Costa Cruise can be confusing for passengers. Pp. 15–18. 

330 Fed. Appx. 892, reversed and remanded. 

SOTOMAYOR, J., delivered the opinion of the Court, in which ROBERTS, 

C. J., and STEVENS, KENNEDY, THOMAS, GINSBURG, BREYER, and ALITO, 

JJ., joined. SCALIA, J., filed an opinion concurring in part and concurring in the judgment. 
_________________ 

_________________ 

Cite as: 560 U. S. ____ (2010) 1 

Opinion of the Court 

NOTICE: This opinion is subject to formal revision before publication in the

preliminary print of the United States Reports. Readers are requested to

notify the Reporter of Decisions, Supreme Court of the United States, Washington, D. C. 20543, of any typographical or other formal errors, in order

that corrections may be made before the preliminary print goes to press. 

SUPREME COURT OF THE UNITED STATES 

No. 09–337 

WANDA KRUPSKI, PETITIONER v. COSTA 

CROCIERE S. P. A. 

ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF 

APPEALS FOR THE ELEVENTH CIRCUIT

[June 7, 2010]

 JUSTICE SOTOMAYOR delivered the opinion of the Court. 

Rule 15(c) of the Federal Rules of Civil Procedure governs when an amended pleading “relates back” to the date 

of a timely filed original pleading and is thus itself timely

even though it was filed outside an applicable statute of 

limitations. Where an amended pleading changes a party 

or a party’s name, the Rule requires, among other things, 

that “the party to be brought in by amendment . . . knew

or should have known that the action would have been 

brought against it, but for a mistake concerning the proper

party’s identity.” Rule 15(c)(1)(C). In this case, the Court 

of Appeals held that Rule 15(c) was not satisfied because

the plaintiff knew or should have known of the proper

defendant before filing her original complaint. The court 

also held that relation back was not appropriate because 

the plaintiff had unduly delayed in seeking to amend. We 

hold that relation back under Rule 15(c)(1)(C) depends on

what the party to be added knew or should have known,

not on the amending party’s knowledge or its timeliness in

seeking to amend the pleading. Accordingly, we reverse

the judgment of the Court of Appeals. 
2 KRUPSKI v. COSTA CROCIERE S. P. A. 

Opinion of the Court 

I 

On February 21, 2007, petitioner, Wanda Krupski,

tripped over a cable and fractured her femur while she

was on board the cruise ship Costa Magica. Upon her

return home, she acquired counsel and began the process 

of seeking compensation for her injuries. Krupski’s passenger ticket—which explained that it was the sole contract between each passenger and the carrier, App. to Pet.

for Cert. 37a—included a variety of requirements for

obtaining damages for an injury suffered on board one of 

the carrier’s ships. The ticket identified the carrier as 

“Costa Crociere S. p. A., an Italian corporation, and all

Vessels and other ships owned, chartered, operated,

marketed or provided by Costa Crociere, S. p. A., and 

all officers, staff members, crew members, independent contractors, medical providers, concessionaires, pilots, suppliers, agents and assigns onboard said Vessels, and the manufacturers of said Vessels and all 

their component parts.” Id., at 27a. 

The ticket required an injured party to submit “written 

notice of the claim with full particulars . . . to the carrier 

or its duly authorized agent within 185 days after the date

of injury.” Id., at 28a. The ticket further required any 

lawsuit to be “filed within one year after the date of injury” and to be “served upon the carrier within 120 days

after filing.” Ibid. For cases arising from voyages departing from or returning to a United States port in which the 

amount in controversy exceeded $75,000, the ticket designated the United States District Court for the Southern 

District of Florida in Broward County, Florida, as the

exclusive forum for a lawsuit. Id., at 36a. The ticket 

extended the “defenses, limitations and exceptions . . . that 

may be invoked by the CARRIER” to “all persons who may 

act on behalf of the CARRIER or on whose behalf the 

CARRIER may act,” including “the CARRIER’s parents, 
Cite as: 560 U. S. ____ (2010) 3 

Opinion of the Court 

subsidiaries, affiliates, successors, assigns, representatives, agents, employees, servants, concessionaires and

contractors” as well as “Costa Cruise Lines N. V.,” identified as the “sales and marketing agent for the CARRIER

and the issuer of this Passage Ticket Contract.” Id., at 

29a. The front of the ticket listed Costa Cruise Lines’ 

address in Florida and stated that an entity called “Costa

Cruises” was “the first cruise company in the world” to

obtain a certain certification of quality. Id., at 25a. 

On July 2, 2007, Krupski’s counsel notified Costa Cruise

Lines of Krupski’s claims. App. 69–70. On July 9, 2007, 

the claims administrator for Costa Cruise requested additional information from Krupski “[i]n order to facilitate 

our future attempts to achieve a pre-litigation settlement.”

App. to Pet. for Cert. 23a–24a. The parties were unable to

reach a settlement, however, and on February 1, 2008—

three weeks before the 1-year limitations period expired—

Krupski filed a negligence action against Costa Cruise, 

invoking the diversity jurisdiction of the Federal District

Court for the Southern District of Florida. The complaint

alleged that Costa Cruise “owned, operated, managed,

supervised and controlled” the ship on which Krupski had

injured herself; that Costa Cruise had extended to its 

passengers an invitation to enter onto the ship; and that

Costa Cruise owed Krupski a duty of care, which it 

breached by failing to take steps that would have prevented her accident. App. 23–26. The complaint further 

stated that venue was proper under the passenger ticket’s 

forum selection clause and averred that, by the July 2007

notice of her claims, Krupski had complied with the 

ticket’s presuit requirements. Id., at 23. Krupski served

Costa Cruise on February 4, 2008. 

Over the next several months—after the limitations 

period had expired—Costa Cruise brought Costa Crociere’s existence to Krupski’s attention three times. First, 

on February 25, 2008, Costa Cruise filed its answer, as-
4 KRUPSKI v. COSTA CROCIERE S. P. A. 

Opinion of the Court 

serting that it was not the proper defendant, as it was 

merely the North American sales and marketing agent for

Costa Crociere, which was the actual carrier and vessel 

operator. Id., at 31. Second, on March 20, 2008, Costa 

Cruise listed Costa Crociere as an interested party in its

corporate disclosure statement. App. to Pet. for Cert. 20a.

Finally, on May 6, 2008, Costa Cruise moved for summary 

judgment, again stating that Costa Crociere was the 

proper defendant. App. 5, 33–38.

On June 13, 2008, Krupski responded to Costa Cruise’s

motion for summary judgment, arguing for limited discovery to determine whether Costa Cruise should be dismissed. According to Krupski, the following sources of

information led her to believe Costa Cruise was the responsible party: The travel documents prominently identified Costa Cruise and gave its Florida address; Costa 

Cruise’s Web site listed Costa Cruise in Florida as the 

United States office for the Italian company Costa Crociere; and the Web site of the Florida Department of State 

listed Costa Cruise as the only “Costa” company registered

to do business in that State. Id., at 43–45, 56–59. Krupski also observed that Costa Cruise’s claims administrator 

had responded to her claims notification without indicating that Costa Cruise was not a responsible party. Id., at 

45. With her response, Krupski simultaneously moved to

amend her complaint to add Costa Crociere as a defendant. Id., at 41–42, 52–54. 

On July 2, 2008, after oral argument, the District Court 

denied Costa Cruise’s motion for summary judgment

without prejudice and granted Krupski leave to amend,

ordering that Krupski effect proper service on Costa Crociere by September 16, 2008. Id., at 71–72. Complying

with the court’s deadline, Krupski filed an amended complaint on July 11, 2008, and served Costa Crociere on

August 21, 2008. Id., at 73, 88–89. On that same date, 

the District Court issued an order dismissing Costa Cruise 
Cite as: 560 U. S. ____ (2010) 5 

Opinion of the Court 

from the case pursuant to the parties’ joint stipulation,

Krupski apparently having concluded that Costa Cruise 

was correct that it bore no responsibility for her injuries. 

Id., at 85–86. 

Shortly thereafter, Costa Crociere—represented by the

same counsel who had represented Costa Cruise, compare 

id., at 31, with id., at 100—moved to dismiss, contending

that the amended complaint did not relate back under 

Rule 15(c) and was therefore untimely. The District Court 

agreed. App. to Pet. for Cert. 8a–22a. Rule 15(c), the

court explained, imposes three requirements before an

amended complaint against a newly named defendant can

relate back to the original complaint. First, the claim 

against the newly named defendant must have arisen “out 

of the conduct, transaction, or occurrence set out—or 

attempted to be set out—in the original pleading.” Fed. 

Rules Civ. Proc. 15(c)(1)(B), (C). Second, “within the 

period provided by Rule 4(m) for serving the summons and 

complaint” (which is ordinarily 120 days from when the

complaint is filed, see Rule 4(m)), the newly named defendant must have “received such notice of the action that it 

will not be prejudiced in defending on the merits.” Rule 

15(c)(1)(C)(i). Finally, the plaintiff must show that, within

the Rule 4(m) period, the newly named defendant “knew 

or should have known that the action would have been 

brought against it, but for a mistake concerning the proper

party’s identity.” Rule 15(c)(1)(C)(ii). 

The first two conditions posed no problem, the court

explained: The claim against Costa Crociere clearly involved the same occurrence as the original claim against 

Costa Cruise, and Costa Crociere had constructive notice 

of the action and had not shown that any unfair prejudice 

would result from relation back. App. to Pet. for Cert. 

14a–18a. But the court found the third condition fatal to 

Krupski’s attempt to relate back, concluding that Krupski

had not made a mistake concerning the identity of the 
6 KRUPSKI v. COSTA CROCIERE S. P. A. 

Opinion of the Court 

proper party. Id., at 18a–21a. Relying on Eleventh Circuit precedent, the court explained that the word “mistake” should not be construed to encompass a deliberate 

decision not to sue a party whose identity the plaintiff 

knew before the statute of limitations had run. Because 

Costa Cruise informed Krupski that Costa Crociere was

the proper defendant in its answer, corporate disclosure

statement, and motion for summary judgment, and yet 

Krupski delayed for months in moving to amend and then

in filing an amended complaint, the court concluded that 

Krupski knew of the proper defendant and made no 

mistake. 

The Eleventh Circuit affirmed in an unpublished per 

curiam opinion. Krupski v. Costa Cruise Lines, N. V., 

LLC, 330 Fed. Appx. 892 (2009). Rather than relying on 

the information contained in Costa Cruise’s filings, all of 

which were made after the statute of limitations had 

expired, as evidence that Krupski did not make a mistake, 

the Court of Appeals noted that the relevant information 

was located within Krupski’s passenger ticket, which she

had furnished to her counsel well before the end of the 

limitations period. Because the ticket clearly identified 

Costa Crociere as the carrier, the court stated, Krupski 

either knew or should have known of Costa Crociere’s 

identity as a potential party.1 It was therefore appropriate to treat Krupski as having chosen to sue one potential 

party over another. Alternatively, even assuming that she 

first learned of Costa Crociere’s identity as the correct

party from Costa Cruise’s answer, the Court of Appeals 

—————— 

1The Court of Appeals stated that it was “imput[ing]” knowledge to 

Krupski. 330 Fed. Appx., at 895. Petitioner uses the terms “imputed

knowledge” and “constructive knowledge” interchangeably in her brief,

while respondent addresses only actual knowledge. Because we reject

the Court of Appeals’ focus on the plaintiff’s knowledge in the first 

instance, see infra, at 8–13, the distinction among these types of

knowledge is not relevant to our resolution of this case. 
Cite as: 560 U. S. ____ (2010) 7 

Opinion of the Court 

observed that Krupski waited 133 days from the time she 

filed her original complaint to seek leave to amend and did 

not file an amended complaint for another month after 

that. In light of this delay, the Court of Appeals concluded 

that the District Court did not abuse its discretion in 

denying relation back.

We granted certiorari to resolve tension among the

Circuits over the breadth of Rule 15(c)(1)(C)(ii),

2 558 U. S. 

___ (2010), and we now reverse. 

II 

Under the Federal Rules of Civil Procedure, an amendment to a pleading relates back to the date of the original 

pleading when: 

“(A) the law that provides the applicable statute of 

limitations allows relation back; 

“(B) the amendment asserts a claim or defense that 

arose out of the conduct, transaction, or occurrence set 

out—or attempted to be set out—in the original plead-

—————— 

2See, e.g., Krupski v. Costa Cruise Lines, N. V., LLC, 330 Fed. Appx. 

892, 895 (CA11 2009) (per curiam) (case below); Rendall-Speranza v. 

Nassim, 107 F. 3d 913, 918 (CADC 1997) (provision does not authorize

relation back where plaintiff “was fully aware of the potential defendant’s identity but not of its responsibility for the harm alleged”); 

Cornwell v. Robinson, 23 F. 3d 694, 705 (CA2 1994) (no relation back 

where plaintiff knew the identities of the responsible defendants and

failed to name them); Goodman v. Praxair, Inc., 494 F. 3d 458, 469–470 

(CA4 2007) (en banc) (rejecting argument that plaintiff’s knowledge of

proper corporate defendant’s existence and name meant that no mistake had been made); Arthur v. Maersk, Inc., 434 F. 3d 196, 208 (CA3

2006) (“A ‘mistake’ is no less a ‘mistake’ when it flows from lack of

knowledge as opposed to inaccurate description”); Leonard v. Parry, 219 

F. 3d 25, 28–29 (CA1 2000) (plaintiff’s knowledge of proper defendant’s

identity was not relevant to whether she made a “ ‘mistake concerning

the identity of the proper party’ ”). We express no view on whether 

these decisions may be reconciled with each other in light of their

specific facts and the interpretation of Rule 15(c)(1)(C)(ii) we adopt 

today. 
8 KRUPSKI v. COSTA CROCIERE S. P. A. 

Opinion of the Court 

ing; or 

“(C) the amendment changes the party or the naming of the party against whom a claim is asserted, if 

Rule 15(c)(1)(B) is satisfied and if, within the period 

provided by Rule 4(m) for serving the summons and 

complaint, the party to be brought in by amendment: 

“(i) received such notice of the action that it will not 

be prejudiced in defending on the merits; and 

“(ii) knew or should have known that the action 

would have been brought against it, but for a mistake 

concerning the proper party’s identity.” Rule 15(c)(1). 

In our view, neither of the Court of Appeals’ reasons for 

denying relation back under Rule 15(c)(1)(C)(ii) finds 

support in the text of the Rule. We consider each reason 

in turn. 

A 

The Court of Appeals first decided that Krupski either 

knew or should have known of the proper party’s identity

and thus determined that she had made a deliberate 

choice instead of a mistake in not naming Costa Crociere

as a party in her original pleading. 330 Fed. Appx., at 

895. By focusing on Krupski’s knowledge, the Court of

Appeals chose the wrong starting point. The question 

under Rule 15(c)(1)(C)(ii) is not whether Krupski knew or

should have known the identity of Costa Crociere as the

proper defendant, but whether Costa Crociere knew or 

should have known that it would have been named as a 

defendant but for an error. Rule 15(c)(1)(C)(ii) asks what 

the prospective defendant knew or should have known 

during the Rule 4(m) period, not what the plaintiff knew 

or should have known at the time of filing her original 
Cite as: 560 U. S. ____ (2010) 9 

Opinion of the Court 

complaint.3 

Information in the plaintiff’s possession is relevant only

if it bears on the defendant’s understanding of whether 

the plaintiff made a mistake regarding the proper party’s 

identity. For purposes of that inquiry, it would be error to

conflate knowledge of a party’s existence with the absence

of mistake. A mistake is “[a]n error, misconception, or 

misunderstanding; an erroneous belief.” Black’s Law 

Dictionary 1092 (9th ed. 2009); see also Webster’s Third

New International Dictionary 1446 (2002) (defining “mistake” as “a misunderstanding of the meaning or implication of something”; “a wrong action or statement proceeding from faulty judgment, inadequate knowledge, or

inattention”; “an erroneous belief”; or “a state of mind not 

in accordance with the facts”). That a plaintiff knows of a 

party’s existence does not preclude her from making a 

mistake with respect to that party’s identity. A plaintiff 

may know that a prospective defendant—call him party 

A—exists, while erroneously believing him to have the 

status of party B. Similarly, a plaintiff may know generally what party A does while misunderstanding the roles 

that party A and party B played in the “conduct, transaction, or occurrence” giving rise to her claim. If the plaintiff

sues party B instead of party A under these circumstances, she has made a “mistake concerning the proper

party’s identity” notwithstanding her knowledge of the 

existence of both parties. The only question under Rule 

—————— 

3Rule 15(c)(1)(C) speaks generally of an amendment to a “pleading”

that changes “the party against whom a claim is asserted,” and it

therefore is not limited to the circumstance of a plaintiff filing an

amended complaint seeking to bring in a new defendant. Nevertheless, 

because the latter is the “typical case” of Rule 15(c)(1)(C)’s applicability,

see 3 Moore’s Federal Practice §15.19[2] (3d ed. 2009), we use this

circumstance as a shorthand throughout this opinion. See also id., 

§15.19[3][a]; Advisory Committee’s 1966 Notes on Fed. Rule Civ. 

Proc. 15, 28 U. S. C. App., pp. 122–123 (hereinafter Advisory Committee’s 1966 Notes). 
10 KRUPSKI v. COSTA CROCIERE S. P. A. 

Opinion of the Court 

15(c)(1)(C)(ii), then, is whether party A knew or should 

have known that, absent some mistake, the action would 

have been brought against him. 

Respondent urges that the key issue under Rule

15(c)(1)(C)(ii) is whether the plaintiff made a deliberate 

choice to sue one party over another. Brief for Respondent

11–16. We agree that making a deliberate choice to sue 

one party instead of another while fully understanding the

factual and legal differences between the two parties is the

antithesis of making a mistake concerning the proper 

party’s identity. We disagree, however, with respondent’s

position that any time a plaintiff is aware of the existence 

of two parties and chooses to sue the wrong one, the

proper defendant could reasonably believe that the plaintiff made no mistake. The reasonableness of the mistake 

is not itself at issue. As noted, a plaintiff might know that 

the prospective defendant exists but nonetheless harbor a

misunderstanding about his status or role in the events

giving rise to the claim at issue, and she may mistakenly 

choose to sue a different defendant based on that misimpression. That kind of deliberate but mistaken choice does 

not foreclose a finding that Rule 15(c)(1)(C)(ii) has been

satisfied. 

This reading is consistent with the purpose of relation 

back: to balance the interests of the defendant protected 

by the statute of limitations with the preference expressed 

in the Federal Rules of Civil Procedure in general, and 

Rule 15 in particular, for resolving disputes on their merits. See, e.g., Advisory Committee’s 1966 Notes 122; 3

Moore’s Federal Practice §§15.02[1], 15.19[3][a] (3d ed. 

2009). A prospective defendant who legitimately believed 

that the limitations period had passed without any attempt to sue him has a strong interest in repose. But 

repose would be a windfall for a prospective defendant 

who understood, or who should have understood, that he 

escaped suit during the limitations period only because 
Cite as: 560 U. S. ____ (2010) 11 

Opinion of the Court 

the plaintiff misunderstood a crucial fact about his identity. Because a plaintiff’s knowledge of the existence of a 

party does not foreclose the possibility that she has made

a mistake of identity about which that party should have

been aware, such knowledge does not support that party’s 

interest in repose.

Our reading is also consistent with the history of Rule

15(c)(1)(C). That provision was added in 1966 to respond 

to a recurring problem in suits against the Federal Government, particularly in the Social Security context.

Advisory Committee’s 1966 Notes 122. Individuals who 

had filed timely lawsuits challenging the administrative

denial of benefits often failed to name the party identified

in the statute as the proper defendant—the current Secretary of what was then the Department of Health, Education, and Welfare—and named instead the United States; 

the Department of Health, Education, and Welfare itself;

the nonexistent “Federal Security Administration”; or a

Secretary who had recently retired from office. Ibid. By 

the time the plaintiffs discovered their mistakes, the 

statute of limitations in many cases had expired, and the 

district courts denied the plaintiffs leave to amend on the

ground that the amended complaints would not relate 

back. Rule 15(c) was therefore “amplified to provide a

general solution” to this problem. Ibid. It is conceivable 

that the Social Security litigants knew or reasonably

should have known the identity of the proper defendant 

either because of documents in their administrative cases 

or by dint of the statute setting forth the filing requirements. See 42 U. S. C. §405(g) (1958 ed., Supp. III). 

Nonetheless, the Advisory Committee clearly meant their

filings to qualify as mistakes under the Rule. 

Respondent suggests that our decision in Nelson v. 

Adams USA, Inc., 529 U. S. 460 (2000), forecloses the 

reading of Rule 15(c)(1)(C)(ii) we adopt today. We disagree. In that case, Adams USA, Inc. (Adams), had ob-
12 KRUPSKI v. COSTA CROCIERE S. P. A. 

Opinion of the Court 

tained an award of attorney’s fees against the corporation

of which Donald Nelson was the president and sole shareholder. After Adams became concerned that the corporation did not have sufficient funds to pay the award, Adams

sought to amend its pleading to add Nelson as a party and 

simultaneously moved to amend the judgment to hold 

Nelson responsible. The District Court granted both

motions, and the Court of Appeals affirmed. We reversed, 

holding that the requirements of due process, as codified

in Rules 12 and 15 of the Federal Rules of Civil Procedure, 

demand that an added party have the opportunity to

respond before judgment is entered against him. Id., at 

465–467. In a footnote explaining that relation back does

not deny the added party an opportunity to respond to the 

amended pleading, we noted that the case did not arise 

under the “mistake clause” of Rule 15(c):4 “Respondent

Adams made no such mistake. It knew of Nelson’s role 

and existence and, until it moved to amend its pleading, 

chose to assert its claim for costs and fees only against

[Nelson’s company].” Id., at 467, n. 1. 

Contrary to respondent’s claim, Nelson does not suggest 

that Rule 15(c)(1)(C)(ii) cannot be satisfied if a plaintiff 

knew of the prospective defendant’s existence at the time 

she filed her original complaint. In that case, there was 

nothing in the initial pleading suggesting that Nelson was 

an intended party, while there was evidence in the record

(of which Nelson was aware) that Adams sought to add 

him only after learning that the company would not be

able to satisfy the judgment. Id., at 463–464. This evi-

—————— 

4The “mistake clause” at the time we decided Nelson was set forth in 

Rule 15(c)(3). 529 U. S., at 467, n. 1; 528 F. R. D. 525, 529 (1991). Rule 

15(c) was renumbered in 2007 without substantive change “as part of 

the general restyling of the Civil Rules,” at which time it received its

current placement in Rule 15(c)(1)(C)(ii). Advisory Committee’s 2007 

Notes on Fed. Rule Civ. Proc. 15, 28 U. S. C. App., p. 37 (2006 ed., 

Supp. II). 
Cite as: 560 U. S. ____ (2010) 13 

Opinion of the Court 

dence countered any implication that Adams had originally failed to name Nelson because of any “mistake concerning the proper party’s identity,” and instead suggested 

that Adams decided to name Nelson only after the fact in

an attempt to ensure that the fee award would be paid. 

The footnote merely observes that Adams had originally 

been under no misimpression about the function Nelson 

played in the underlying dispute. We said, after all, that 

Adams knew of Nelson’s “role” as well as his existence. 

Id., at 467, n. 1. Read in context, the footnote in Nelson is 

entirely consistent with our understanding of the Rule:

When the original complaint and the plaintiff’s conduct 

compel the conclusion that the failure to name the prospective defendant in the original complaint was the result

of a fully informed decision as opposed to a mistake concerning the proper defendant’s identity, the requirements

of Rule 15(c)(1)(C)(ii) are not met. This conclusion is in 

keeping with our rejection today of the Court of Appeals’

reliance on the plaintiff’s knowledge to deny relation back. 

B 

The Court of Appeals offered a second reason why Krupski’s amended complaint did not relate back: Krupski had 

unduly delayed in seeking to file, and in eventually filing,

an amended complaint. 330 Fed. Appx., at 895. The 

Court of Appeals offered no support for its view that a 

plaintiff’s dilatory conduct can justify the denial of relation 

back under Rule 15(c)(1)(C), and we find none. The Rule 

plainly sets forth an exclusive list of requirements for

relation back, and the amending party’s diligence is not 

among them. Moreover, the Rule mandates relation back 

once the Rule’s requirements are satisfied; it does not 

leave the decision whether to grant relation back to the

district court’s equitable discretion. See Rule 15(c)(1) (“An 

amendment . . . relates back . . . when” the three listed 

requirements are met (emphasis added)). 
14 KRUPSKI v. COSTA CROCIERE S. P. A. 

Opinion of the Court 

The mandatory nature of the inquiry for relation back 

under Rule 15(c) is particularly striking in contrast to the

inquiry under Rule 15(a), which sets forth the circumstances in which a party may amend its pleading before

trial. By its terms, Rule 15(a) gives discretion to the

district court in deciding whether to grant a motion to

amend a pleading to add a party or a claim. Following an

initial period after filing a pleading during which a party 

may amend once “as a matter of course,” “a party may

amend its pleading only with the opposing party’s written 

consent or the court’s leave,” which the court “should 

freely give . . . when justice so requires.” Rules 15(a)(1)– 

(2). We have previously explained that a court may consider a movant’s “undue delay” or “dilatory motive” in

deciding whether to grant leave to amend under Rule 

15(a). Foman v. Davis, 371 U. S. 178, 182 (1962). As the 

contrast between Rule 15(a) and Rule 15(c) makes clear,

however, the speed with which a plaintiff moves to amend 

her complaint or files an amended complaint after obtaining leave to do so has no bearing on whether the amended 

complaint relates back. Cf. 6A C. Wright, A. Miller, & M. 

Kane, Federal Practice and Procedure §1498, pp. 142–143, 

and nn. 49–50 (2d ed. 1990 and Supp. 2010).

Rule 15(c)(1)(C) does permit a court to examine a plaintiff’s conduct during the Rule 4(m) period, but not in the

way or for the purpose respondent or the Court of Appeals 

suggests. As we have explained, the question under Rule 

15(c)(1)(C)(ii) is what the prospective defendant reasonably should have understood about the plaintiff’s intent in

filing the original complaint against the first defendant.

To the extent the plaintiff’s postfiling conduct informs the

prospective defendant’s understanding of whether the 

plaintiff initially made a “mistake concerning the proper 

party’s identity,” a court may consider the conduct. Cf. 

Leonard v. Parry, 219 F. 3d 25, 29 (CA1 2000) (“[P]ostfiling events occasionally can shed light on the plaintiff’s 
Cite as: 560 U. S. ____ (2010) 15 

Opinion of the Court 

state of mind at an earlier time” and “can inform a defendant’s reasonable beliefs concerning whether her omission 

from the original complaint represented a mistake (as 

opposed to a conscious choice)”). The plaintiff’s postfiling

conduct is otherwise immaterial to the question whether

an amended complaint relates back.5 

C 

Applying these principles to the facts of this case, we

think it clear that the courts below erred in denying relation back under Rule 15(c)(1)(C)(ii). The District Court 

held that Costa Crociere had “constructive notice” of 

Krupski’s complaint within the Rule 4(m) period. App. to 

Pet. for Cert. 15a–17a. Costa Crociere has not challenged 

this finding. Because the complaint made clear that Krupski meant to sue the company that “owned, operated, 

managed, supervised and controlled” the ship on which 

she was injured, App. 23, and also indicated (mistakenly) 

that Costa Cruise performed those roles, id., at 23–27, 

Costa Crociere should have known, within the Rule 4(m) 

period, that it was not named as a defendant in that complaint only because of Krupski’s misunderstanding about 

which “Costa” entity was in charge of the ship—clearly a

“mistake concerning the proper party’s identity.” 

Respondent contends that because the original complaint referred to the ticket’s forum requirement and

presuit claims notification procedure, Krupski was clearly 

aware of the contents of the ticket, and because the ticket 

identified Costa Crociere as the carrier and proper party 

—————— 

5Similarly, we reject respondent’s suggestion that Rule 15(c) requires

a plaintiff to move to amend her complaint or to file and serve an

amended complaint within the Rule 4(m) period. Rule 15(c)(1)(C)(i)

simply requires that the prospective defendant has received sufficient

“notice of the action” within the Rule 4(m) period that he will not be

prejudiced in defending the case on the merits. The Advisory Committee Notes to the 1966 Amendment clarify that “the notice need not be

formal.” Advisory Committee’s 1966 Notes 122. 
16 KRUPSKI v. COSTA CROCIERE S. P. A. 

Opinion of the Court 

for a lawsuit, respondent was entitled to think that she

made a deliberate choice to sue Costa Cruise instead of 

Costa Crociere. Brief for Respondent 13. As we have 

explained, however, that Krupski may have known the 

contents of the ticket does not foreclose the possibility that

she nonetheless misunderstood crucial facts regarding the 

two companies’ identities. Especially because the face of

the complaint plainly indicated such a misunderstanding,

respondent’s contention is not persuasive. Moreover, 

respondent has articulated no strategy that it could reasonably have thought Krupski was pursuing in suing a

defendant that was legally unable to provide relief. 

Respondent also argues that Krupski’s failure to move

to amend her complaint during the Rule 4(m) period 

shows that she made no mistake in that period. Id., at 

13–14. But as discussed, any delay on Krupski’s part is

relevant only to the extent it may have informed Costa

Crociere’s understanding during the Rule 4(m) period of 

whether she made a mistake originally. Krupski’s failure

to add Costa Crociere during the Rule 4(m) period is not

sufficient to make reasonable any belief that she had 

made a deliberate and informed decision not to sue Costa 

Crociere in the first instance.6 Nothing in Krupski’s conduct during the Rule 4(m) period suggests that she failed 

to name Costa Crociere because of anything other than a 

mistake. 

It is also worth noting that Costa Cruise and Costa 

—————— 

6The Court of Appeals concluded that Krupski was not diligent

merely because she did not seek leave to add Costa Crociere until 133 

days after she filed her original complaint and did not actually file an

amended complaint for another a month after that. 330 Fed. Appx., at 

895. It is not clear why Krupski should have been found dilatory for

not accepting at face value the unproven allegations in Costa Cruise’s

answer and corporate disclosure form. In fact, Krupski moved to

amend her complaint to add Costa Crociere within the time period

prescribed by the District Court’s scheduling order. See App. 3, 6–7; 

Record, Doc. 23, p. 1. 
Cite as: 560 U. S. ____ (2010) 17 

Opinion of the Court 

Crociere are related corporate entities with very similar

names; “crociera” even means “cruise” in Italian. Cassell’s 

Italian Dictionary 137, 670 (1967). This interrelationship

and similarity heighten the expectation that Costa Crociere should suspect a mistake has been made when Costa 

Cruise is named in a complaint that actually describes 

Costa Crociere’s activities. Cf. Morel v. DaimlerChrysler 

AG, 565 F. 3d 20, 27 (CA1 2009) (where complaint conveyed plaintiffs’ attempt to sue automobile manufacturer 

and erroneously named the manufacturer as DaimlerChrysler Corporation instead of the actual manufacturer,

a legally distinct but related entity named DaimlerChrysler AG, the latter should have realized it had not been 

named because of plaintiffs’ mistake); Goodman v. Praxair, Inc., 494 F. 3d 458, 473–475 (CA4 2007) (en banc) 

(where complaint named parent company Praxair, Inc., 

but described status of subsidiary company Praxair Services, Inc., subsidiary company knew or should have 

known it had not been named because of plaintiff’s mistake). In addition, Costa Crociere’s own actions contributed to passenger confusion over “the proper party” for a 

lawsuit. The front of the ticket advertises that “Costa 

Cruises” has achieved a certification of quality, App. to

Pet. for Cert. 25a, without clarifying whether “Costa

Cruises” is Costa Cruise Lines, Costa Crociere, or some 

other related “Costa” company. Indeed, Costa Crociere is 

evidently aware that the difference between Costa Cruise

and Costa Crociere can be confusing for cruise ship passengers. See, e.g., Suppa v. Costa Crociere, S. p. A., No. 

07–60526–CIV, 2007 WL 4287508, *1, (SD Fla., Dec. 4,

2007) (denying Costa Crociere’s motion to dismiss the

amended complaint where the original complaint had 

named Costa Cruise as a defendant after “find[ing] it

simply inconceivable that Defendant Costa Crociere was

not on notice . . . that . . . but for the mistake in the original Complaint, Costa Crociere was the appropriate party 
18 KRUPSKI v. COSTA CROCIERE S. P. A. 

Opinion of the Court 

to be named in the action”).

In light of these facts, Costa Crociere should have

known that Krupski’s failure to name it as a defendant in

her original complaint was due to a mistake concerning

the proper party’s identity. We therefore reverse the 

judgment of the Court of Appeals for the Eleventh Circuit

and remand the case for further proceedings consistent

with this opinion. 

It is so ordered. 
_________________ 

_________________ 

Cite as: 560 U. S. ____ (2010) 1 

Opinion of SCALIA, J. 

SUPREME COURT OF THE UNITED STATES 

No. 09–337 

WANDA KRUPSKI, PETITIONER v. COSTA 

CROCIERE S. P. A. 

ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF 

APPEALS FOR THE ELEVENTH CIRCUIT

[June 7, 2010]

 JUSTICE SCALIA, concurring in part and concurring in 

the judgment. 

I join the Court’s opinion except for its reliance, ante, at 

10–11, 15, n. 5, on the Notes of the Advisory Committee as

establishing the meaning of Federal Rule of Civil Procedure 15(c)(1)(C). The Advisory Committee’s insights into

the proper interpretation of a Rule’s text are useful to the

same extent as any scholarly commentary. But the Committee’s intentions have no effect on the Rule’s meaning.

Even assuming that we and the Congress that allowed the 

Rule to take effect read and agreed with those intentions, 

it is the text of the Rule that controls. Tome v. United 

States, 513 U. S. 150, 167–168 (1995) (SCALIA, J., concurring in part and concurring in judgment).