Worldcon (the World Science Fiction Convention) is the annual gathering of science fiction and fantasy fans, writers, artists, musicians and other creators, first held in New York City in 1939. Worldcon is held in a different city and organized by a different volunteer organization each year.
Worldcon 76 will be held in San Jose, California, in August 2018. It's being organized by a committee sponsored by San Francisco Science Fiction Conventions, Inc., a California public benefit corporation.
Worldcon 75 is being held in Helsinki, Finland in August 2017, and is being organized by a completely different group. Its website is www.worldcon.fi