The unexpected death of Supreme Court Justice Antonin Scalia on February 13, 2016—in the middle of the Supreme Court's October 2015 term—has prompted questions about the process for filling the vacancy and how the Court will proceed in hearing cases and issuing opinions. These questions pertain to the constitutional role of the President and Senate in filling Supreme Court vacancies, whether and when the President and the Senate must act, and how the Supreme Court may proceed in hearing cases and issuing opinions with a vacant seat. This report provides answers to frequently asked legal questions about filling Supreme Court vacancies. Additionally, other CRS products address other procedural and historical issues surrounding Supreme Court vacancies. See CRS Report R44400, The Death of Justice Scalia: Procedural Issues Arising on an Eight-Member Supreme Court , by [author name scrubbed]; CRS Report R44235, Supreme Court Appointment Process: President's Selection of a Nominee , by [author name scrubbed]; CRS Report R44236, Supreme Court Appointment Process: Consideration by the Senate Judiciary Committee , by [author name scrubbed]; CRS Report R44234, Supreme Court Appointment Process: Senate Debate and Confirmation Vote , by [author name scrubbed]; CRS Report R44083, Appointment and Confirmation of Executive Branch Leadership: An Overview , by [author name scrubbed] and [author name scrubbed]; and CRS Report RL31980, Senate Consideration of Presidential Nominations: Committee and Floor Procedure , by [author name scrubbed]. The unexpected death of Supreme Court Justice Antonin Scalia on February 13, 2016—in the middle of the Supreme Court's October 2015 term—has prompted questions about the process for filling the vacancy and how the Court may proceed in hearing cases and issuing opinions. In particular, these questions pertain to the constitutional role of the President and Senate in filling Supreme Court vacancies, when the P resident and the Senate must act, and how the Supreme Court may continue hearing cases and issuing opinions with a vacant seat. This report provides answers to frequently asked legal questions about filling Supreme Court vacancies. The Supreme Court is not required to have nine Justices. The Constitution is silent on the number. Historically, by statute Congress has set the number of Justices for the Court. Currently, that number is nine: one Chief Justice plus eight Associate Justices. But only six Justices are needed for a quorum. In the event that the Court is scheduled to hold a session but there is not a quorum, the Justices (or the clerk or deputy clerk) may announce that the Court will not meet until a quorum is restored. The nature of the President's prerogatives under the Appointments Clause is unclear. The Obama Administration has taken the position that the President has a constitutional obligation to nominate and appoint a Supreme Court Justice when there is a vacancy. The Constitution's Appointments Clause states that the President " shall nominate, and by and with the advice and consent of the Senate, shall appoint ... judges of the Supreme Court." Courts have generally construed the word "shall," in the Constitution and federal statutes, to impose a mandatory obligation. For instance, when interpreting the word "shall" in Article III of the Constitution, the Supreme Court stated that "[t]he word shall, is a sign of the future tense, and implies an imperative mandate, obligatory upon those to whom it is addressed." However, the Court has not clarified when in the future the President needs to act. Supreme Court precedent regarding vacancies in other positions subject to presidential appointment suggests that the President has significant discretion as to when a vacancy "shall" be filled. The Senate's prerogatives under the Appointments Clause are even less clear. The Appointments Clause states that the President "shall nominate, and by and with the advice and consent of the Senate , shall appoint ... judges of the Supreme Court." Unlike the duties spelled out for the President, the Appointments Clause does not provide that the Senate "shall" give its advice and consent, nor does it expound on what the Senate must do to give its advice and consent—two distinct tasks. Additionally, the Supreme Court has not fully interpreted the specific terms "advice" and "consent" as they are used in the Appointments Clause, so it is not entirely clear what actions the Senate must take, assuming any action were seen to be required. For instance, during a 1975 symposium on "Advice and Consent on Supreme Court Nominations," then-Senator James Abourezk noted that, "[w]hile the 'consent' aspect of the Senate's constitutional role is thus readily discernable, the same cannot be so easily said of the Senate's duty to give its 'advice' on a Supreme Court appointment" or "to state precisely just how that duty is to be exercised institutionally." In the past, the Senate has provided its advice and consent by various means, ranging from committee hearings to a vote on the Senate floor. Accordingly, there is disagreement in the legal community about the Senate's role in presidential appointments. Although there is no doubt that the Senate has a constitutional role in the appointments process, much of the disagreement surrounds how robust that role is, especially concerning advice. Some view the Senate's role to give advice as an active one, in which failing to consider a nominee at all would violate its constitutional obligations. For example, one former Senator has stated that "[a]mong all the responsibilities of a United States Senator, none is more important than the duty to participate in the process of selecting judges and justices to serve on the federal courts." The Obama Administration similarly contends that the Senate has a constitutional obligation to act—a position previously taken by the George W. Bush Administration. Conversely, others assert that the Senate has no constitutional obligation to act once the President nominates a new Justice, contending, for example, that the lack of "shall" in the advice-and-consent text in Article II creates only a prerequisite for the President's nominee to be confirmed by the Senate. Additionally, at least one Senator has reportedly taken the view that "[i]t's up to the Senate to decide how we do our job with regard to" advice and consent, suggesting that interpreting the Senate's role in the Appointments Clause could be seen as a political question for the legislative branch to decide. However, absent a definitive resolution by the judicial branch—which would be unlikely —settlement of occasional disputes between the President and Senate regarding their respective roles in the Supreme Court nomination process seem likely to be resolved though interbranch negotiation and accommodation. The Constitution's Recess Appointments Clause states that "[t]he President shall have Power to fill up all Vacancies that may happen during the Recess of the Senate, by granting Commissions which shall expire at the End of their next session." The Supreme Court has not addressed whether the Constitution permits the President to appoint an Article III judge (including Supreme Court Justices) using a recess appointment, and thus the issue remains unsettled. The Appointments Clause, though, which precedes the Recess Appointments Clause, authorizes the President to appoint "judges of the supreme Court." Accordingly, some courts have concluded that the Recess Appointments Clause encompasses filling Article III judicial vacancies. For example, the Eleventh Circuit opined in Evans v. Stephens that President George W. Bush lawfully appointed a judge to the U.S. Court of Appeals during an 11-day Senate recess. Despite reaching this conclusion, the court noted tension between Article III—which provides for tenure during "good behaviour" —and appointing Article III judges under the Recess Appointments Clause, for whom the appointment would expire at the end of the congressional session in which the recess appointment was made. Additionally, when the Supreme Court declined to review Evans , then-Supreme Court Justice Stevens wrote to emphasize that the denial of certiorari was not a ruling on the merits that confirms the Eleventh Circuit's decision, perhaps suggesting that he had doubts about the veracity of the ruling. Assuming, however, that the President could use the Recess Appointments Clause to appoint a new temporary Supreme Court Justice, the Senate typically must be in recess for at least 10 days for the recess appointment to be valid. Presidential nominations under the Appointments Clause expire at the end of the congressional term during which they are made. But nothing in the Constitution or in any federal law prohibits the President from re-nominating a Supreme Court nominee who was rejected or never voted on during the Senate's term. For example, President Eisenhower first nominated John Marshall Harlan II to be a Supreme Court Justice on November 9, 1954, but the Senate did not vote on the nomination. President Eisenhower re-nominated Harlan on January 10, 1955, and the newly constituted Senate confirmed the nomination. In general, cases may be reheard in one of two ways. First, parties may petition the Supreme Court for rehearing after the Court issues an adverse ruling on the merits or denies granting review for a case (sought through a petition for a writ of certiorari or extraordinary writ). For cases already decided on the merits, a majority of the Court must grant the petition for rehearing, which would be considered only at the request of one of the Justices who concurred in the Court's judgment on the merits. Second, the Court typically will order cases to be reheard if the Justices conclude that they cannot resolve the case before the Court's summer recess. For example, the Court, on its own initiative, decided to rehear three cases that had been argued after Chief Justice Rehnquist's death but before the vacancy had been filled.