A developmental league in basketball is a lower level professional league that focuses on developing younger players who work their way into better leagues. This can also be a league where lower level players play for their career and do not typically move up in the higher leagues.
The G-League is the primary developmental league for the National Basketball Association. It was formerly known as the D-League, standing for developmental, before Gatorade became the majority sponsor in 2017 and changed the name as part of their advertising campaign.
28 NBA teams have G-League affiliates, while the Denver Nuggets and Portland Trail Blazers do not. The benefit of having a designated affiliate is that when teams assign players to the G-League, they are able to send them to a coaching system that they have hired rather than a random team.
The most common way for G-League players to play in the NBA is through two-way contracts. Two way contracts designate that a player will be apart of the G-League team for most of the season, but can be called up to the NBA for a limited number of days. Depending on how well they perform during this stint determines whether they could receive a full-time contract.
Pascal Siakam, Jeremy Lin, and Hassan Whiteside are all players who have had successful NBA careers after playing in this developmental league.
While not directly considered developmental leagues for the NBA, there are many other locations that players have come from where they harnessed their skills before playing at the highest level of professional basketball. Spain's Liga ACB has produced players such as Pau and Marc Gasol and Kristaps Porzingis. The Turkish Super League and Australian National Basketball League are two other well known organizations.