A string quartet is a musical ensemble consisting of four string players – two violin players, a viola player and a cellist. It is also a musical composition written to be performed by such a group. The string quartet is one of the most prominent chamber ensembles in classical music; most major composers from the mid 18th century onwards having written string quartets. Some string quartets ensembles play together for many years and become established and promoted as an entity in a similar way to an instrumental soloist or an orchestra.