The precise time and place of the first science fiction convention is a matter of some dispute. Sometime in 1936, a group of British fans made plans to have an organized gathering, with a planned program of events in a public venue in early 1937. However, on October 22, 1936, a group of six or seven fans from New York City, including David Kyle and Frederik Pohl, traveled by train to Philadelphia, PA, where, for several hours they visited a similar number of local fans at the house of Milton A. Rothman. They subsequently declared that event to be the first "science fiction convention." This small get-together set the stage for a follow-up event held in New York, in February, 1937, where "30 or 40" fans gathered at Bohemian Hall in Astoria, Queens. Attendees at this event included James Blish, Charles D. Hornig, Julius Schwartz, and Willis Conover. This event came to be known as the "Second Eastern" and set the stage for the successful Third Eastern held in Philadelphia on October 30, 1937 and the subsequent Fourth Eastern held on May 29, 1938, which attracted over 100 attendees to a meeting hall in Newark, NJ and designated itself as "The First National Science Fiction Convention." It was at this event that a committee was named to arrange the first World Science Fiction Convention in New York in 1939; formalizing planning that had begun at the Third Eastern. The "First National", which included the participation of a number of well-known New York editors and professionals from outside fan circles, was a milestone in the evolution of science-fiction conventions as a place for science-fiction (SF) professionals, as well as fans, to meet their colleagues in person.
On January 3, 1937, the British fans held their long-planned event at the Theosophical Hall in Leeds. Around twenty fans, including Eric Frank Russell and Arthur C. Clarke, attended. To this day, many fan historians, especially those in the United Kingdom, contend that the Philadelphia meeting was a convention in name only, whereas other fan historians point out that many similar gatherings since then have been called "conventions" without eliciting any disagreement.
Nevertheless, by 1939, American fans had organized sufficiently to hold, in conjunction with the 1939 World's Fair, the first "World Science Fiction Convention," in New York City. Subsequent conventions were held in Chicago in 1940 and Denver in 1941. Like many cultural events, it was suspended during World War II. Conventions resumed in 1946 with the hosting of the World Science Fiction Convention in Los Angeles, California. The first Worldcon held outside the United States was Torcon I in Toronto in 1948; since then, Worldcons have been held in Britain, Germany, the Netherlands, Canada, Australia, and in 2007, Japan, although the majority of Worldcons are still held within the United States.