The World Esperanto Congress is an annual Esperanto convention. It has the longest tradition among international Esperanto conventions, with an almost unbroken run for 119 years. The congresses have been held since August 5, 1905, every year, except during World War I, World War II, and the COVID-19 pandemic. Since the 1920s, the Universal Esperanto Association has been organizing these congresses.

Esperanto is the world's most widely spoken constructed international auxiliary language. Created by L. L. Zamenhof in 1887, it is intended to be a universal second language for international communication, or "the international language". Zamenhof first described the language in Dr. Esperanto's International Language, which he published under the pseudonym Doktoro Esperanto. Early adopters of the language liked the name Esperanto and soon used it to describe his language. The word esperanto translates into English as "one who hopes".