Esperanto is a constructed auxiliary language. Its creator was L. L. Zamenhof, a Polish eye doctor. He created the language to make international communication easier. His goal was to design Esperanto in such a way that people can learn it much more easily than any other national language.

At first, Zamenhof called the language La Internacia Lingvo, which means "The International Language" in Esperanto. Soon, people began calling it by the simpler name Esperanto, which means "one who hopes". That name comes from Doktoro Esperanto ("Doctor who hopes"), which is what Zamenhof called himself in his first book about Esperanto.

There are people who speak Esperanto in many countries and in all the major continents. No one knows exactly how many people now speak Esperanto in the world. Most sources say that there are between several hundred thousand and two million Esperanto speakers. A few people grew up speaking Esperanto as their first language. There may perhaps be around 2,000 of these people. Therefore, Esperanto is the most-used constructed language in the world.

A person who speaks or supports Esperanto is often called an "Esperantist".