Speculation was released under the title Zenith for the first six issues, which lasted from 1963 till 1964. It was then called Zenith Speculation for issues 7 to 13, between 1964 and 1966, during which time Peter Weston was also publishing the apazine Nexus. After 1966, the fanzine assumed its final identity, Speculation.
Contributors to Speculation include Brian Aldiss, Poul Anderson, Greg Benford, Jsmes Blish (The Planeteer), John Boston, John Brosnan (Big Scab), John Brunner, Ken Bulmer (Science Fantasy News), F.M. Busby (Cry of the Nameless), Richard Delap, Harlan Ellison (Science Fantasy Bulletin), John Foyster, Richard Gordon, Tim Hildebrand, Lang Jones, Fritz Leiber, Robert A.W. Lowdnes, David Masson, Archie Mercer (Vector), Beryl Mercer (Link, Oz), Sandra Miesel, Michael Moorcock (Typo, A Fanzine Called Eustace), Larry Niven, Andy Offut, Alexei Panshin, Joe Patrizio (Ipso Facto), John J. Pierce, writing on Cordwainer Smith, Martin Pitt, Charles Platt (Beyond), Frederik Pohl (The International Observer of Science and Science Fiction), Chris Priest, David Redd, Bob Rickard, Ben Solon Harry Warner, Jr. (Horizons), and Ian Williams (Maya).
Covers were by Richard Bergeron (Warhoon) (#25), Vincent diFate (#29), Jack Gaughan (#21), Ivor Latto (#24, #26), Bob Rickard (#20, #30), Paula Yates, Ames (#33).
Artwork was contributed by Jim Cawthorn, Eddie Jones, Vincent DiFate, among others.
Speculation also featured an interview with writer J.G. Ballard by Jannick Storm.
Letters came Rick Brooks (Nargothrond), Pamela Bulmer, Terry Carr (Lighthouse), Graham Charnock (Wrinkled Shrew), Samuel R. Delany, Philip Jose Farmer, Bruce Gillespie (SF Commentary), Graham Hall, Sam Moskowitz (New Fandom), Alexei Panshin, and Donald Wollheim, among others
A series of "Speculation Conferences" were also organised, adopting a similarly "sercon" approach to science fiction analysis. It won the very first Nova Award for Best Fanzine, in 1973.