Professional basketball clubs in Europe can compete in a number of different competitions, including national leagues, regional (multi-national) leagues, and continental competitions. It is therefore possible for clubs from some countries to take part in several levels of competition in the same season. Clubs usually qualify for European competitions through performance in their national or regional leagues, with the exception of wild cards.
There are currently four competitions which are branded as Europe-wide, two controlled by Euroleague Basketball, and two by FIBA Europe. Clubs which compete in these competitions also play in their national and/or regional leagues. Clubs usually qualify for these competitions based on their performance in the national or regional leagues in the previous season.
The EuroLeague is a competition with currently 16 permanent members. It has historically been the most prestigious competition in European basketball and is widely recognised as the top-tier league in Europe.
The EuroCup is Euroleague Basketball's secondary competition, and currently made up of 24 teams from around Europe. Clubs from over 30 countries have taken part. The two finalists of the EuroCup qualify for the next season's EuroLeague.
The Basketball Champions League, which began in 2016, is FIBA Europe's highest competition. Initially, FIBA established EuroLeague in 1958 but never trademarketed the name which was later taken over by Euroleague Basketball. The Basketball Champions League involves around 40 teams; to date, clubs from over 20 countries have taken part.
The Europe Cup is FIBA Europe's secondary competition. Up to 32 teams compete, and the teams which did not enter in the Basketball Champions League regular season have the option to drop down into the regular season of the Europe Cup. As of 2019, clubs from over 30 national federations have taken part.
In addition to national leagues in individual countries, there are leagues which include clubs from several countries.
The ABA League, commonly called the Adriatic League, began in 2001, and consists of clubs from the former Yugoslavia (Bosnia and Herzegovina, Croatia, Montenegro, North Macedonia, Serbia and Slovenia). At different times, the league has also included clubs from Bulgaria, the Czech Republic, Hungary, and Israel. Clubs generally also compete in their own national leagues in the same season, after the conclusion of the ABA League season. The winner of the league qualifies for the next season's EuroLeague.
The VTB United League is made up of mostly Russian clubs, as well as a smaller number of clubs from nearby countries - currently Belarus, Estonia, Latvia, Kazakhstan and Poland. It serves as the top division of the Russian national league system. One club from the league qualifies for the next season's EuroLeague, in addition to CSKA Moscow, which holds a EuroLeague license.
Other multi-national leagues in Europe have included the Baltic Basketball League (2004-2018), the Central European Basketball League (2008–2010), and the Balkan International Basketball League (began in 2008).
Each country generally has its own league system, with various divisions which involve promotion and relegation, as well as playoffs following the regular season.
The Spanish Liga ACB contributes the most, three to four clubs to the EuroLeague each season. Other leagues among the strongest include Russia's VTB United League, Turkey's BSL, the Greek Basket League, Italy's LBA, the LNB Pro A in France and the ABA League.