Building and managing a complete U-21 team is one of the requirements for clubs participating in the ISL. Those U-21 teams will participate in the Indonesia Super League U-21 which is held in parallel with the main competition. In 2009-10, Persib Bandung U-21 team won the league, then Persela U-21 won the title two years in a row (2011 & 2012).
Before 2008, the highest level of professional soccer competition in Indonesia was the Premier Division. It used the combination format of double round-robin first round and single eliminations second round. Indonesia Super League uses the double round-robin competition format.
Considering only these two ISL editions, Persipura Jayapura is considered as the best achieving clubs, since they could finish the first and second position consecutively. Considering the whole history of top level of professional soccer league in Indonesia, Persebaya Surabaya, Persik Kediri along with Persipura Jayapura are the best achievers, winning the competitions twice.
The first edition of ISL used the same format for foreign players as the previous edition of top layer league in Indonesia, which allows club to have 4 foreign players from any countries without further restrictions. Only 3 of them are allowed to play together in a match.
Since the 2014 edition, Indonesian FA has applied a new restriction as known as "3+1" format, in which at least 1 of 4 foreign players in every club are originated from Asian countries. Furthermore, those foreign players need to conform with the following condition:
Players from European or American countries should have played in the second division (third layer of their respective competition system).
Players from Asian countries whose club competed in the AFC Champions League and AFC Cup should have played in (at least) in the first division (second layer of their respective competition system).
Players from African countries and Asian countries (whose club did not competed in the AFC Champions League and AFC Cup) should have played (at least) in the premier/super league (highest layer of their respective competition system).
Players from Southeast Asian countries should be in their national team.
In 2010-2011 edition, Indonesian FA introduced a new restriction regarding registration of new foreign players from African countries. Players from African countries who have never played before in Indonesia Super League shall be an international player for his country. The respective players have to show formal evidences that they have played for their country in official FIFA matches. Players failed to show such evidences will not get permit to play in Indonesia Super League 2010-2011.