The Esperanto Museum (German: Esperantomuseum; Esperanto: Esperantomuzeo) in Vienna, Austria was founded in 1927 by Hofrat Hugo Steiner and was incorporated into the Austrian National Library as an independent collection in 1928. Today it is at the same time museum, library, documentation centre and archive. It accommodates the biggest collection of artificial languages in the world and a linguistic research library for language planning. Since 2005, the Esperanto Museum and Collection of Planned Languages (German: Esperantomuseum und Sammlung für Plansprachen, Esperanto: Esperantomuzeo kaj kolekto por planlingvoj) has been located in the baroque Palais Mollard-Clary.
The holdings of the collection consist of more than 35,000 library volumes, 3,100 periodical titles, 3,000 cultural artifacts, 10,000 autographs and manuscripts, 22.000 photographs and photographic negatives, 1,200 posters and 40,000 pamphlets. In all, approximately 500 various planned languages are documented, of which the most important are Esperanto and Interlingua.