Esperanto is a constructed international auxiliary language. Its creator, L. L. Zamenhof, published the first book detailing Esperanto, Unua Libro, under the pseudonym Dr. Esperanto, in 1887. Since then, Esperanto has been the most widely used constructed auxiliary language in the world, with speakers in over 120 countries.

Esperanto has a relatively simple grammar, with only 16 rules governing word order. The language is highly regular, and features a large number of words that are easily guessed from their roots. This makes Esperanto easier to learn than many natural languages.

Esperanto has a culture and community associated with it, including literature, music, and film. There are also Esperanto-themed games, websites, and other online resources.

The Esperanto flag consists of a green star on a white background. The star represents the hope of Esperanto speakers for a better world, while the green represents the language's environmental friendliness.