A "lame duck" session of Congress is one that takes place after the election for the next Congress has been held but before the current Congress has reached the end of its constitutional term. Since 1935, the constitutional term of a Congress has begun on January 3 of each odd-numbered year and has ended on January 3 of the next odd-numbered year. As a result, any meeting of Congress that occurs between the congressional election in November of an even-numbered year and the following January 3 is a lame duck session. The significant characteristic of a lame duck session is that its participants are the sitting Members of the existing Congress, not those who will be entitled to sit in the new Congress. For the purposes of this study, a lame duck session commences on the first day of consecutive sessions following an election. It ends on the day of final sine die adjournment. The expression "lame duck" was originally applied in 18 th century Britain to bankrupt businessmen, who were considered "lame," like a game bird injured by shot. By the 1830s, the usage had been extended to officeholders whose service already had a known termination date. In current American usage, for instance, a President is considered a "lame duck" after his successor has been elected and also whenever he is known not to be a candidate for reelection. Members of Congress in similar circumstances are also considered "lame ducks." The expression may be applied to Members who are known not to be seeking reelection as well as to those who have been defeated. In particular, however, after an election of Congress, all the Members who did not gain reelection can be described as lame ducks until the term of the new Congress starts. When the previously sitting Congress, which includes these Members, meets after the election, this session is called a lame duck session. The possibility of a lame duck session of Congress in the modern sense began in 1935, when the Twentieth Amendment to the Constitution took effect. Under this amendment, ratified in 1933, the terms of Members begin and end on January 3 of odd-numbered years. Congress convenes in a regular session on January 3 of each year unless it passes a law changing the date. Any meeting of Congress after election day (in November of even-numbered years) but before the following January 3 is a lame duck session. This report examines only the lame duck sessions that have occurred since 1935, not those that, as explained in the following section, occurred regularly before that time. Through 2016, there were 21 lame duck sessions. Between 1935 and 1998, however, lame duck sessions occurred in 12 of 32 Congresses; in contrast, they have occurred in every one of the nine Congresses from 1999 through 2016. In order to present the differences between the two periods, this report discusses data from the 20 th and 21 st centuries separately. The Constitution originally provided that the regular sessions of Congress begin annually on the first Monday in December. Congress began and ended its term on March 4 of odd-numbered years. Congressional elections were still generally held in November of even-numbered years. Members of Congress were elected in an even-numbered November, but the term for the new Congress did not begin until the following (odd-numbered) March. However, a new Congress often did not convene its first session until the following December, 13 months after it was first elected. This session of Congress typically continued until the summer of the following even-numbered year. Congress would then adjourn until the next regular session prescribed by the Constitution, beginning in the following even-numbered December. When this session convened, however, the next Congress would already have been elected in the intervening even-numbered November. Under these arrangements, the last session of every Congress was always a lame duck session. One purpose of the Twentieth Amendment was to change the timing that caused every Congress to hold its last session after an election. Sometimes a Congress would convene its first session as early as March, especially when a new President was entering office. This became the first session of a Congress, and the odd-year December session became its second session. The final session of the Congress, beginning in the even-year December, was the third session. This final session, however, would still be a lame duck session of the old Congress, because it would convene at a time when the new Congress had already been elected in November but had not yet begun its term of office. Under the Twentieth Amendment, lame duck sessions can still occur but only as a result of specific actions undertaken either by the Congress already sitting or by the President. A lame duck session may occur under the following circumstances: (1) by a previously enacted law prescribing an additional session of Congress; (2) following a recess within a session but spanning the election; (3) under authority granted to the leadership at the time of a contingent adjournment or recess of the session; (4) by continuing to meet, perhaps in pro forma sessions, throughout the period spanning the election; and (5) in response to a presidential proclamation calling an extraordinary session. Although some of these methods have been used rarely and others not at all, each helps to illuminate the constitutional arrangements that make lame duck sessions possible and the conditions in which they may operate. The following sections describe each method and indicate its implications. Although the "lame duck sessions" that have occurred before and after 1935 are both "lame duck" in the same sense, they are not "sessions" in the same sense. Formally, a session of Congress ends when Congress adjourns sine die . In Latin, the phrase means "without day," or without a day designated to return; adjourning sine die closes the final day of a legislative session. An adjournment sine die , therefore, means that Congress is not scheduled to meet again until the day set by the Constitution (or by law) for its next session to convene. The Constitution authorizes Congress to set its own adjournment date without the involvement of the President, unless the two houses cannot agree. Congress therefore authorizes a sine die adjournment by concurrent resolution. This form of measure requires adoption by both houses but no action by the President. When Congress adjourns sine die in an election year, it is not scheduled to meet again before the term of the new Congress begins. Before the sine die adjournment, however, Congress could provide by law that an additional session of the old Congress convene on a date after the election. Nevertheless, since 1935, Congress has never convened a lame duck session as a new, third session of the old Congress. When a Congress has decided to continue meeting after an election, its usual practice has been not to adjourn sine die but simply to recess its existing session for a period spanning the election. It can then reconvene at a date still within the constitutional term of the sitting Congress. Congress authorizes a session recess in the same way it authorizes a sine die adjournment: by adopting a concurrent resolution. The Constitution provides that "Neither House, during the Session of Congress, shall, without the Consent of the other, adjourn for more than three days." Thus, each chamber must consent to the adjournment of the other. Congress achieves this end with concurrent resolutions, which require action by both houses. Unlike a sine die adjournment, however, a recess of the session does not terminate the existing session of Congress; instead, the previously existing session resumes. Nevertheless, the phrase "lame duck session" has persisted as a way of referring to any post-election meeting of the old Congress, even though it does not designate a distinct (i.e., third) session of Congress . Lame duck sessions may also occur when the House or Senate leadership uses contingent authority to reconvene the respective chambers "if the public interest shall require." Since 1935, it has become common for Congress to include contingent authority for the leadership to reconvene the House and Senate in the concurrent resolutions providing for either a session recess or a sine die adjournment. Congress may use this contingent authority as a means to return early from a recess spanning an election. Any portion of the reconvened session that occurs after the election would be considered a lame duck session. Since the Twentieth Amendment took effect, however, this course of action has not been taken. Congress may also use contingent authority to reconvene after a sine die adjournment. In this case, the sine die character of the adjournment becomes definitive only if the leadership does not exercise this authority by the time the next session of Congress is slated to convene. If the authority is exercised, the existing session of the old Congress resumes, and the previous adjournment turns out not to have been sine die . Any post-election portion of this continuation of the previous session of Congress would be considered a lame duck session. The Speaker of the House has twice used authority of this kind to reconvene the chamber in a post-election continuation of a session that had previously been terminated by a conditional sine die adjournment. These lame duck sessions of the House occurred in 1998 (105 th Congress) and 2008 (110 th Congress). No lame duck session of the Senate has been reconvened pursuant to authority of this kind. One reason why leadership might call Congress back is to avoid a "pocket veto." The Constitution provides that if the President vetoes a bill while Congress is in session, he must return the vetoed bill to Congress so that Congress may attempt to override a veto. If the last regular session of a Congress has adjourned sine die , however, the Congress that passed the bill can no longer convene to override the veto, so the veto automatically becomes final. Under these conditions, the Constitution empowers the President to prevent the bill from becoming law simply by not returning it.