MOMus–Museum of Modern Art–Costakis Collection, Modern art museum in Thessaloniki, Greece.

The MOMus Museum of Modern Art houses the Costakis Collection, one of the largest assemblages of Russian avant-garde artworks outside Russia. It operates exhibition spaces within the Lazariston Monastery complex in Thessaloniki, displaying works from 1900 to 1930.

The museum was founded in December 1997, when Thessaloniki was European Capital of Culture, by a law passed in the Greek Parliament under culture minister Evangelos Venizelos. Its first president was Dimitris Fatouros and its first director Miltiadis Papanikolaou. The Costakis Collection reached the building in 1998 and was formally bought by the Greek state on 31 March 2000 for 14,200,000,000 drachmas. In 2018 the State Museum of Contemporary Art joined four other Thessaloniki visual arts museums under the MOMus umbrella and took its present name.

The collection focuses on Russian avant-garde artworks from the early 20th century, showing experimental pieces rarely seen in Western Europe. Visitors can discover works reflecting the artistic upheaval of this era and documenting the development of modern art movements.

The museum offers permanent and rotating exhibitions, guided tours, workshops, and educational programs for various visitors. It is wise to allow enough time to appreciate both the artworks and the architectural features of the historic building fully.

The Costakis Collection entered the museum in 1998 and was formally acquired by the Greek state on 31 March 2000 for 14,200,000,000 drachmas, after Culture Minister Evangelos Venizelos secured it for the newly founded institution. An international committee of experts first assessed its authenticity and value. It numbers 1,275 works, including paintings, drawings, constructions and ceramics.