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The Hector Hodler Library is one of the largest Esperanto libraries, with approximately 30,000 books, with periodicals, manuscripts, photos, music, and other collections. It occupies three rooms in the central office of the Universal Esperanto Association in Rotterdam, Netherlands.
The library is originated in Switzerland, when the Swiss Esperanto Society opened a library in 1908. In 1912, the library came to the possession of Hector Hodler, the founder of Universal Esperanto Association (UEA). After his death, it was under UEA in Switzerland. After World War II, in 1947, the library was renamed the Hector Hodler Library in his honour. Along with the translocation of the UEA headquarters to Rotterdam, the library was settled there in 1960.
Other major collections of Esperanto books are: International Esperanto Museum, Montagu C. Butler Library, Centre de documentation et d'étude sur la langue internationale, and the German Esperanto Library.