A recess appointment occurs when the President of the United States fills a vacant Federal position during a recess of the United States Senate. The commission or appointment must be approved by the Senate by the end of the next session, or the position becomes vacant again. Recess appointments are authorized by Article II, Section 2 of the U.S. Constitution: "The 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."

According to Henry B. Hogue, at the Government and Finance Division of the Congressional Reference Service, "Recent Presidents have made both intersession (between sessions or Congresses) and intrasession (during a recess within a session) recess appointments. Intrasession recess appointments were unusual, however, prior to the 1940s. Intrasession recess appointments have sometimes provoked controversy in the Senate, and there is also an academic literature that has drawn their legitimacy into question." Law Professor Michael B. Rappaport argues that the original meaning of the clause required that if an office is vacant while the Senate is in session, the Constitution expects the President to make an advice and consent appointment at that time. He also maintains the original meaning allows recess appointments to be made only during intersession recesses, which during the early days of the country lasted between 6 and 9 months and therefore required recess appointments to prevent important offices from remaining unfilled for long periods; the current interpretation allows appointments during recesses too brief to justify bypassing the Senate.

Historically, presidents tended to make recess appointments when the Senate was adjourned for lengthy periods. Since World War II, presidents have sometimes made recess appointments when Senate opposition appeared strong, hoping that the appointee might prove himself in office and allow opposition to dissipate. Most recently, however, as partisanship on Capitol Hill has grown, recess appointments have tended to solidify opposition to whoever is appointed.