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Page Number: 7

Cite as:  598 U. S. ____ (2023) 

1 

Opinion of the Court 

NOTICE:  This opinion is subject to formal revision before publication in the 
United  States  Reports.  Readers  are  requested  to  notify  the  Reporter  of 
Decisions,  Supreme  Court  of  the  United  States,  Washington,  D. C.  20543, 
pio@supremecourt.gov, of any typographical or other formal errors. 

SUPREME COURT OF THE UNITED STATES 

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No. 21–1496 
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TWITTER, INC., PETITIONER v. MEHIER 
TAAMNEH, ET AL. 

ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF 
APPEALS FOR THE NINTH CIRCUIT 

[May 18, 2023] 

JUSTICE THOMAS delivered the opinion of the Court. 
Under  18  U. S. C.  §2333,  United  States  nationals  who 
have been “injured . . . by reason of an act of international 
terrorism” may sue for damages.  §2333(a).  They are not 
limited  to  suing  the  individual  terrorists  or  organizations
that directly carried out the attack, however.  That is be-
cause §2333(d)(2) also imposes civil liability on “any person
who aids and abets, by knowingly providing substantial as-
sistance, or who conspires with the person who committed
such an act of international terrorism.”  Victims of terrorist 
acts  therefore  may  seek  to  recover  from  those  who  aided 
and abetted the terrorist act that injured them. 

The  plaintiffs  (who  are  respondents)  contend  that  they 
have stated a claim for relief under §2333(d)(2).  They were
allegedly injured by a terrorist attack carried out by ISIS. 
But  plaintiffs  are  not  suing  ISIS. 
Instead,  they  have
brought suit against three of the largest social-media com-
panies in the world—Facebook, Twitter (who is petitioner),
and  Google  (which  owns  YouTube)—for  allegedly  aiding 
and abetting ISIS.  As plaintiffs allege, ISIS has used de-
fendants’  social-media  platforms  to  recruit  new  terrorists