The Collection of the Working Class Movement Museum results from a fusion of three Prague museums – the Klement Gottwald Museum, the V. I. Lenin Museum and the Julius Fučík Museum, which were taken over and completed by the Working Class Movement Museum in 1990. For the reason of securing the completeness of the Collection, the Working Class Movement Museum donated it to the National Museum in 2014. The Collection of hundreds of thousands of items consists of collectibles (e.g. works of visual art, posters, military objects, flags and standards, honours and documents of social events and also photographic and film materials), archive records (some personal possessions of Klement Gottwald, Antonín Zápotocký, Julius and Gusta Fučík, a collection of the written materials and of the small prints and archives of the original museums) and library items (publications from the 19th and 20th centuries focused on the history of the social movements and the processes). This paper presents both the origins and the content of the Collection and summarises the process of its change of location and deposition and also the creation of the new concept regarding the treatment of the museum funds.