The Encyclopedia of Science Fiction is currently in its third edition and encompasses over 4 million words about all things SF. It is published online in collaboration with Gollancz and the SF Gateway.
This new version follows thirty-five years of work (on and off), and is heavily expanded from previous editions. The first being under the GeneralEditorship of Peter Nicholls in 1979; and the 1993 Second Edition, being edited by John Clute (the most prolific contributor to date) and Peter Nicholls. The third edition is based on the 1995 CD-Rom “printing” and it has David Langford as the primary technical editor as well as a contributor.
As a resource for fan studies, the encyclopedia is useful because it includes a whole section titled “Culture” including separate categories/tags for “Publication”, “Fan”, “Award”, and “International”. It is by no means comprehensive but it does offer information not always found elsewhere, especially regarding SF fanzines and Big Name Fans (of literature especially).