The Prime League was the reserve and youth team soccer league of Singapore's S.League. Teams involved in the league are primarily made up of youth players from the S.League clubs. The Prime League was founded in 1997. S.League clubs are required to participate, and clubs who do not play at S.League level are also eligible to enter. Each club is allowed to register 1 foreign player for their Prime League teams. The foreign players must be aged between 18 and 21 at the point of registration and are not eligible to play in the S.League. Prime League sides also take part in the FA Cup competition.