Fundamento de Esperanto

Fundamento de Esperanto (English: Foundation of Esperanto) is a 1905 book by L. L. Zamenhof, in which the author explains the basic grammar rules and vocabulary that constitute the basis of the constructed language Esperanto. On August 9, 1905, it was made the only obligatory authority over the language by the Declaration of Boulogne at the first World Esperanto Congress. Much of the content of the book is a reproduction of content from Zamenhof's earlier works, particularly Unua Libro.