The World Congress of Esperanto (in Esperanto: Universala Kongreso de Esperanto) has the longest tradition among international Esperanto conventions, with an almost unbroken run of nearly a hundred years. The Congresses have been held since 1905 every year, except during World Wars I and II. The Universal Esperanto Association has therefore about 100 years of experience in congress organizing.

These congresses take place every year and gather on average about 2000 participants (since World War II it has varied from 800 to 6000 depending on the venue). The average number of countries represented is about 60. Some specialized organizations also gather a few hundred participants in their annual meetings. The Universal Congress usually takes place in the last week of July or first week of August, beginning and ending on a Saturday (8 days in total).