As of 2015, 68 teams compete in the NCAA men's basketball tournament. The tournament has increased in size several times since its inception, including a 1985 expansion to include 64 teams. This format held for over 20 years before expanding to the current 68-team field in 2011.
At the time of the first NCAA men's basketball tournament in 1939, only eight teams participated. Public interest in the event has grown considerably in the intervening years, which may be part of the reason why the NCAA occasionally expands the tournament to allow more and more teams to play. At one point in the event's history, the number of teams in the tournament doubled in the span of a decade: after five expansions, the field grew from 32 teams in 1975 to 64 in 1985.