The National Basketball Association (NBA) was founded in 1946 and began operations as the Basketball Association of America (BAA). In 1949, the BAA merged with the National Basketball League (NBL), absorbing the latter's teams and rebranding as the NBA; the 1949–50 NBA season marked the first following the merger. NBA win–loss records include the wins and losses recorded during a team's playing time in the BAA. Defunct BAA/NBA franchises are also accounted for. However, NBA win–loss records do not include the wins and losses recorded during a team's playing time in the American Basketball Association (ABA), despite the 1976 ABA–NBA merger.
In regular season play, the Boston Celtics have the highest win–loss percentage, with 3,710–2,511 (.596).