The World Esperanto Congress (Esperanto: Universala Kongreso de Esperanto) has the longest tradition among international Esperanto conventions, with an almost unbroken run of more than a hundred years. The congresses have been held since 1905 every year, except during World Wars I and II. Since the 1920s, the World Esperanto Association has been organizing these congresses.
These congresses take place every year and, over the 30 years from 1985 through 2014, have gathered an average of 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 World 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). For many years ILERA has operated an amateur radio station during the conventions.
Until 1980, meetings were held in Europe and the United States, with the exception of Japan in 1965. Since then, other countries have been Brazil, Canada, China, Cuba, South Korea, Australia, Israel, Vietnam and Argentina.
The attendance at each World Esperanto Congress from the 1st in 1905 until the 100th in 2015.