The Encyclopedia of Science Fiction is an English language reference work on SF, first published in 1979. The second edition appeared in 1993, followed by an expanded CD-ROM in 1995. In October 2011, the third edition was made available for free online: http://www.sf-encyclopedia.com/.
The editors for the first two editions were John Clute (billed as Associate Editor in 1979) and Peter Nicholls (billed as General Editor in 1979). The principal editors for the third edition are Clute and Dave Langford, with Nicholls now billed as Editor Emeritus and Graham Sleight as Managing Editor.