Moderna galerija was founded in 1947 as a museum of modern art. The initiative for the erection of a national museum and exhibition ground devoted to modern art, as opposed to the National Gallery, was made by Izidor Cankar, an art historian, critic, writer and diplomat, while the construction was funded from the heritage of industrialist Dragotin Hribar. The new museum building was designed in the 1930's by Edvard Ravnikar, one of the most renowned Slovenian architects of the 20th century.
The project was the result of his thorough consideration of the needs and functions of a contemporary art museum at the time. Ravnikar conceived a formally neutral building, a "white cube" in which exhibition spaces were hierarchically equal, while the central hall, from which one had access to the other rooms, would allow independent installation of various exhibitions and collections. The architecture reveals the influences of Ravnikar's teacher, Jože Plečnik, which can be seen particularly in the facade and windows, while the rationalistic and functionalistic elements derive from the architectural modernism of the legendary Le Corbusier, under whom Ravnikar worked for a brief period in 1939.
The construction works, almost completed by 1941, were brought to a halt at the outbreak of war and the building served as a military warehouse until 1945.
The works were resumed after the end of the war. Moderna galerija was formally founded by decree of the government of the People's Republic of Slovenia on 30 December 1947, which took effect on 3 January 1948. The first director of the gallery was painter Gojmir Anton Kos (1948-49), succeeded by Karel Dobida (1952-57). Zoran Kržišnik, who had actually been the manager of Moderna galerija since 1947, took the position in 1957 and held it until 1986. From 1986 to 1992, the director of Moderna galerija was Jure Mikuž, who was succeeded by Zdenka Badovinac in 1992.
Lively exhibition activities began immediately after the founding, and the first permanent exhibition presenting Slovenian art from Impressionism until 1950 opened in 1951. Moderna galerija has held a series of important exhibitions and other presentations, many of them pivotal in the development of Slovene art.
In Socialist times, Moderna galerija did not quite fit the dominant, i.e. Western, paradigm of a museum of modern art, although it followed its example within the scope of its possibilities. Although it followed the canons of Modernism in terms of architecture and the models of presentation of art, it used them as a means for evading ideological pressure. Interestingly, it was the formalism of Modernism with its apparent neutrality and lack of interest in current social problems that ultimately best suited the then authorities.
Up until the collapse of the former Yugoslavia, Moderna galerija systematically focused on collecting works by Slovenian artists. Its exhibition policy, too, was directed primarily at presenting Slovenian art production, the most prominent exception being the International Biennial of Graphic Arts launched in 1955; in 1985, its organization was taken over by the International Centre of Graphic Arts, which became an independent institution at that time.
With Slovenia's independence in 1991, Moderna galerija became the principal national institution of modern and contemporary art and an increasingly active link between the local and the international, in particular Central and Eastern European, contexts. One of the results of this orientation is the international collection Arteast 2000+ established in 2000.
Modern Gallery (MG+) closed down in 2007 due to a complete overhaul of the building carried out by the architectural firm Bevk Perović arhitekti selected in a public tender. The renovation work was completed in the autumn of 2009. The listed building retained all of its former characteristic features; the only major changes occurred in the basement that now houses up-to-date storerooms and a photographic studio as well as two new spaces for visitors, an auditorium and a café.
Due to its shortage of space, Moderna galerija was allotted the use of another building by the Ministry of Culture of the Republic of Slovenia as early as 1995: one of the buildings in the former Yugoslav People's Army barracks in Metelkova Street. In 2000, even before the renovation, the Arteast 2000+ collection was presented there, auguring the concept of the future museum of contemporary art.
The building housing the Museum of Contemporary Art Metelkova (+MSUM) is part of a former military barracks complex that was initially erected for the Austro-Hungarian army and used by the Yugoslav People's Army after the Second World War. In 1991, after the Yugoslav People's Army left Slovenia, the state earmarked the southern part of the complex to be used for museums, while the northern part was squatted by artists and activists who founded the Metelkova City Autonomous Cultural Centre in 1993. The Ministry of Culture designated the south part as a museum quarter, renovating first the buildings of the Slovenian Ethnographic Museum, the outstation of the National Museum of Slovenia, and lastly, the building Moderna galerija had conceived as a space for contemporary art. The renovation of the barracks and the design of the museum quarter is the work of the architectural firm Groleger arhitekti.
When the Museum of Contemporary Art Metelkova (+MSUM) was finally opened in late November 2011, Moderna galerija (MG+MSUM) was at last able to reorganise its work in two large units as planned: Moderna galerija (MG+, museum of modern art), which has remained in the building at Tomšičeva Street, and the Museum of Contemporary Art Metelkova (+MSUM) located in the former military barracks complex at Metelkova Street.
The difference between Moderna galerija (MG+) and +MSUM is based on the historical development of Moderna galerija, its collections, exhibition policies and the cultural-political contexts on the one hand, and, on the other, on the need to re-evaluate modernism and articulate contemporaneity as something that essentially differs from both Modernism and Postmodernism and describes a particular condition of art, its institutions, and social circumstances.
 Some of these are: the exhibition of Slovene Impressionism in 1949, which was an important victory over extreme ideological dogma; the exhibition of works by Riko Debenjak and Stane Kregar in 1953, which opened up the question of Abstract art; the important Henry Moore exhibition in 1955, which gave a powerful stimulus to Modernist tendencies; and the first international graphic art exhibition in the same year, which launched the important tradition of international biennials of graphic art. Crucial for the avant-garde movement in the 1960's were the exhibitions of the OHO group in 1968 and in 1969. The 1976 exhibition of the three abstract painters, Tomo Podgornik, Tugo Šušnik and Andraž Šalamun, introduced a new understanding of the Abstract painting and its tradition. In 1979, Moderna galerija staged an important historical exhibition Slovene Art 1945 - 1978 that was followed in 1986 by Expressionism and the New Objectivity in Slovenia.