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.

Fundamento de Esperanto consists of four parts: a foreword, a grammar section, a collection of exercises, and a dictionary.

With the exception of the foreword, almost everything in the Fundamento comes directly from Zamenhof's earlier works, primarily Unua Libro.

[1] The grammar and dictionary sections of the Fundamento are in five national languages: French, English, German, Russian, and Polish.

If anyone deviates from the rules and models given in the said work, he can never justify himself with the words "thus desires or advises the author of Esperanto".