List of defunct and relocated Major League Baseball teams

Throughout the history of Major League Baseball, numerous franchises have moved or become defunct. Many of these franchises played in the National League (NL) and the American League (AL), the two existing major leagues, but other franchises played in one of the eleven major leagues that ultimately went defunct. The classification of the major leagues is based on Major League Baseball's recognition of historical leagues.

Major league baseball emerged in the 1870s, and four major leagues, including the NL, played at least one season of baseball in the nineteenth century. During this period, dozens of franchises were founded, but most went defunct, leaving just twelve NL franchises by the 1892 season. After four of the twelve NL franchises went defunct following the 1899 season, the American League emerged in 1901 with several newly founded franchises. The Federal League (FL) challenged the primacy of the American League and the National League for two seasons, but the FL and all of its franchises went defunct after the 1915 season. Numerous Negro leagues operated during the first half of the twentieth century; seven leagues that operated from 1920 to 1948 were later recognized as major leagues by Major League Baseball.

The Baltimore Orioles went defunct after the 1902 season, representing the most recent time that an NL or AL team ceased operations. No NL or AL team would go defunct or relocate until the relocation of the Boston Braves to Milwaukee following the 1952 season. Several teams moved over the next twenty years, often to the Southern or Western United States, with the last such move taking place in 1971 when the Washington Senators became the Texas Rangers. The Montreal Expos became the Washington Nationals in 2005, the first move in three decades. In 2025, the Oakland Athletics plan to temporarily move to West Sacramento, California, and brand themselves as simply the "A's" and "Athletics" with no city name attached, until they permanently move to Las Vegas in 2028 or later when their new ballpark is completed.^[1]