NBA G-League

On June 13, 2000, NBA Commissioner David Stern and deputy commissioner Russ Granik announced the formation of the National Basketball Development League, to begin play in November 2001, with players required to be at least twenty years old. This was not the first time the league had their own minor league system, as they had used the Continental Basketball Association (CBA) as a developmental league for over two decades. The NBA had attempted to buy the CBA in March 2000, but they were rejected.

The league began its play as the National Basketball Development League (NBDL) in the 2001–02 season; the eight franchises were all located in the southeastern United States (in Virginia, North Carolina, South Carolina, Alabama, and Georgia). Each team logo was given NBDL branding that was differentiated by team colors.

Eight players were called up to the NBA during the season, which included Chris Andersen, the first player drafted by a NBDL team. The league made sponsorship deals with Reebok and television broadcasting deals with ESPN2 and Fox Sports South to broadcast select games during the first season (such as the NBDL Finals), which made them one of few minor league operations to have nationally televised games. The Greenville Groove won the first NBDL championship on April 8, 2002, after winning game 2 over the North Charleston Lowgators. The league saw an average attendance of 1,640 fans per game, lower than what the NBA expected.

In 2005, the league's name was changed to NBA Development League (NBA D-League) as part of the new collective bargaining agreement with the NBA and a bid to appeal to more fans by showing the connection to the NBA. In the same offseason, Southwest Basketball, LLC led by David Kahn received league permission to operate four new teams. Southwest Basketball purchased three existing franchises and one expansion team: the Albuquerque Thunderbirds, Austin Toros, Fort Worth Flyers, and Tulsa 66ers. The Arkansas RimRockers were also added from the ABA for the 2005–06 season. In February 2006, the D-League expanded to California with the addition of the Bakersfield Jam. Two months later, the league announced that four teams from the CBA were joining the league: the Dakota Wizards, Sioux Falls Skyforce, Idaho Stampede, and a team originally slated for CBA expansion, the Colorado 14ers. Shortly after, the league announced expansion teams in the Anaheim Arsenal and the Los Angeles D-Fenders. The D-Fenders were the first D-League team to be directly owned by an NBA parent team, the Los Angeles Lakers.

However, the westward expansion contributed to the contraction of the NBA-owned Roanoke Dazzle and Fayetteville Patriots for that season. The Florida Flame suspended operations due to arena scheduling difficulties. After the 2006–07 season, there would be no more teams in the southeastern United States until the 2016 expansion team, the Greensboro Swarm.

After the 2006 to 2009 expansions, the league membership was fairly consistent with few relocations and suspensions. In 2009, the Houston Rockets entered into the first single-affiliation partnership, called the hybrid model, with the Rio Grande Valley Vipers. This began a trend of NBA and D-League teams entering into single-affiliation agreements of both the hybrid and parent-team owned varieties. With more NBA involvement, the league once again began to expand and spread its footprint.

By 2015, the last multiple-affiliate team, the Fort Wayne Mad Ants, was purchased by the Indiana Pacers, leading to the first season where all D-League teams were affiliated with only one NBA team. As there were no longer any unaffiliated D-League teams left, the remaining NBA teams began purchasing expansion franchises or hybrid partnership teams and placing them near the parent team. In 2015, the Toronto Raptors placed their own team, Raptors 905, in the Greater Toronto Area in Mississauga, Ontario. In 2016, the D-League expanded by three more NBA parent club-owned teams for the largest D-League expansion since 2007. The Charlotte Hornets created the Greensboro Swarm, the Brooklyn Nets created the Long Island Nets, and the Chicago Bulls created the Windy City Bulls.

In the 2017–18 season, the D-League entered into a multi-year partnership with Gatorade and rebranded as the NBA Gatorade League, which was officially shortened to "NBA G League" prior to the season. It also continued its membership changes with the relocation of the Erie BayHawks to Lakeland, Florida, as the Lakeland Magic, a new Erie BayHawks franchise, and expansions in the Agua Caliente Clippers in Ontario, California (now known as the San Diego Clippers), the Memphis Hustle in Southaven, Mississippi, and the Wisconsin Herd in Oshkosh, Wisconsin. The Los Angeles D-Fenders would also re-brand to the South Bay Lakers.

In December 2017, the NBA and the live-streaming website Twitch announced that they would broadcast G League games on Twitch. Games have also been aired on the ESPN+ subscription service.

For the 2019–20 season, the G League began to offer select contracts to players who are not yet eligible to enter the NBA draft. Since 2006, players must be at least 19 years old by the end of the calendar year, creating what became known as the one-and-done rule where players would play one season of college basketball and then leave for the NBA. The new select contract was an alternative for players who do not want to or cannot attend a college, with players earning up to $125,000 per season. The league launched its prospects team, the NBA G League Ignite, in 2020. The G-League Ignite team folded after the 2023–2024 season.

Following the COVID-19 pandemic-curtailed 2019–20 season, the G League postponed the start of the following season. In January 2021, the league announced it would play all games at Walt Disney World in Orlando, Florida, using the same isolation bubble as the 2020 NBA Bubble. Many teams opted out of participation, with only 17 of the 28 teams from the 2019–20 season plus the new Ignite prospects team choosing to take part in the abbreviated bubble season beginning in February 2021.