There are 3 on-court officials in an NBA game. They work as a three-person officiating crew, traditionally designated as the crew chief, referee, and umpire.
The officials move around the court using a three-person rotation system. Their positioning helps them observe plays near the ball, monitor off-ball contact, judge out-of-bounds calls, and identify violations such as traveling, carrying, or illegal screens. Each official has overlapping responsibilities, so a call is not limited strictly to one person’s area.
The NBA has used three referees as its standard on-court system since 1988, when the league moved away from a two-referee crew. The change gave officials better coverage of the increasingly fast and physical style of professional basketball.
The three referees are not the only people involved in officiating a game. Additional personnel handle duties at the scorer’s table, while replay officials and the NBA Replay Center assist with reviews. Those roles are off the court, so they do not change the answer to this question.