The NBA draft is a major annual event in which the 30 franchises in the National Basketball Association select new players for their teams. Eligibility rules for prospective players have changed several times during the history of the league. No player may sign with the NBA until they are 19 years or older. Players who have played at least one year of college basketball are eligible for the NBA draft; this has been colloquially called the one-and-done rule, with such players called "one-and-done players".