The ULEB (acronym of the French Union des Ligues Européennes de Basket, in English Union of European Leagues of Basketball) was founded in 1991 with the aim to help the cooperation and development of European professional basketball leagues. Its headquarters are located in Barcelona, Spain.

The ULEB started in 1991 with Lega Basket A (Italy), Asociación de Clubs de Baloncesto (Spain), and Ligue Nationale de Basketball (France), and were joined in 1996 by Hellenic Basketball Clubs Association (Greece) and Liga dos Clubes de Basquetebol (Portugal). In 1999, the Basketball League Belgium (Belgium), British Basketball League (England), and Ligue Nationale de Basket (Switzerland) were added.

ULEB then expanded with the Deutsche Basketball Bundesliga (BBL) of Germany, Federatie Eredivisie Basketballclubs (Netherlands), and Polska Liga Koszykówki (Poland) in 2001. The Adriatic Basketball Association (sanctions the NLB League in the area) was added in February 2002, while October 2002 brought along the Österreichische Basketball Bundesliga (Austria), with the June 2003 membership of the Lietuvos Krepšinio Lyga (Lithuania), the 2004 membership of the Asociace M. Prvoligovych Klubu (Czech Republic), and in July 2005, the Basketball Superleague of Israel joined the ULEB.

In 2000, the ULEB decided to break from FIBA and begin the new Euroleague in 2001, featuring a five-game series (instead of the one-game final), but that was dropped after one year. ULEB also broke away from the FIBA and adopted rules closer to the NBA, with the NBA's jump ball and 24-second rules being the first to be adopted, in 2002 and 2003, respectively. The hope was the ULEB would play with rules which would favour players, and spectators, which the FIBA did not feature.

In 2004, the ULEB adopted rule changes which made their game similar to the NBA. The jump ball rule, which was the NBA rule, would remain similar to the NBA (no possession arrow, unlike FIBA), and NBA-type rules regarding position of the ball in the final two minutes following a time out (center line) and block and charge fouls within 1.22 metres (4') within the basket were added. LEGA A also adopted an instant replay rule which led to the championship being decided by instant replay as a field goal made in the final second of the game which determined if a team had won or had been forced to a deciding game had to be reviewed for minutes by officials.

For 2005, FIBA decided to make the Euroleague part of the FIBA championships, FIBA rules would replace the NBA-type rules, eliminating the jump ball and block-charge arc.