Basketball leagues are structured similarly to other major sports leagues. There are teams made up by an owner, a front office, coaching staff, and players. On top of the teams there are front office members for the league, including a commissioner.
Basketball leagues have staff that work in the management sector. They oversee the operations of the league and do their best to keep things running smoothly. The most well known position among the management is the league commissioner. The commissioner is in charge of everything and has the final say in all matters.
After the regular season, a "postseason" or "playoffs" in some cases occurs. There are several different ways for this to play out depending on the basketball league. Some teams make use of a bracket format where teams compete in a single elimination tournament, while others crown their champion based on only the regular season. The number of teams that qualify for each postseason is different for each league as well.
Given the popularity of basketball there are many leagues that exist all over the world. There are professional leagues, semi-pro leagues, amateur leagues, and developmental leagues.
The NBA is the most famous basketball league, and is located in the United States. It is made up of 29 teams from various American cities, and one team (Toronto Raptors) from Canada. There are 16 teams that make the playoffs and compete for the NBA Finals to win the Larry O'Brien Trophy.
The G-League is a developmental league for the NBA. NBA teams have affiliated G-League teams, and can bring players up or even sign them to a two-way contract (they can play in
both leagues). The G-League recently was renamed from its previous name of the D League.
There are many different leagues all across Europe. Each country tends to have at least one league where players from all over the world play in. One of those leagues is named the Euroleague, and it contains 16 club teams from all across Europe.
The WNBA is the professional women's basketball league in The United States. There are 12 teams, all of which are in The United States. It first began in 1997 and has been focused on reaching a larger audience in the following years.
Both the NCAA (men's college basketball) and NCAAW (women's college basketball) are collegiate leagues made up of amateur players (students in college). The players play for their respective schools and universities without payment. The leagues however are viewed as a stepping stone to get to the NBA and WNBA.
At this point with established leagues, teams have long since been assigned to a league. That wasn't always the case though. Leagues begin with multiple rich risk takers coming together, with each choosing to own a team and deal with the expenses that came with it. The leagues that they formed contained the teams that each owner is representing.
Leagues can also add teams (expansion teams) when they feel there are untapped markets. In the NBA, The New Orleans Hornets (now The New Orleans Pelicans) were added as recently as 2002! The addition of teams is decided by the league and has to be agreed upon by the team owners.