The Mainstage Series features fully staged productions of musicals by emerging and established authors.

In recent years, most have been world, American, or New York premieres. Each production typically runs seven performances per week for five weeks. Some productions have transferred to commercial off-Broadway or Broadway runs, and many have received further productions in regional, stock, and university theatres. The York's productions have been regularly recognized with Drama Desk, Outer Critics Circle, OBIE, and Lucille Lortel nominations and awards. Numerous shows have been recorded as original cast albums. Directors, designers, cast, and musicians are drawn from among the best talent on and off-Broadway, whether established or new.