Music Theatre in the Ruhr is the venue for performing opera, operetta, musical theatre and ballet in Gelsenkirchen, Germany. It opened on 15 December 1959; it is listed since 1997 as a protected cultural monument. The building offers two performance spaces: the Large House with 1,008 seats and about 200 performances per year, and the Small House with 336 seats and about 120 annual performances. In contrast to the building's outside cubic appearance, the auditoria use a more curved design.

The building was designed by Werner Ruhnau. The cubic outer shell of the Large House is formed by a 4,500 m2 glass facade, which gives view into the interior and the cylindric casing of the auditorium and its stairways, and the two monumental sculptures by the French artist Yves Klein.