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, Carl Brandon, Jr., 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, Harry Harrison, Tim Hildebrand, Terry Jeeves (ERG), Lang Jones, Fritz Leiber, Robert A.W. Lowdnes, David Masson, Ian McAuley, 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), Bruce Pelz, 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, Robert Silverberg, Ben Solon, Tony Sudbery, Harry Warner, Jr. (Horizons), and Ian Williams (Maya).
Covers were by Ames (#33), Richard Bergeron (Warhoon) (#25), Jom Cawthorn (#10), Vincent diFate (#29), Jack Gaughan (#21), Jim Groves (#12), Ivor Latto (#24, #26), Riccardo Leveghi (#14), Ken McIntyre (#13), Bob Rickard (#16, #20, #30), Pamela Yates (#15), Joseph Zajackazowski (#11).
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), Edmond Cooper, Samuel R. Delany, Sven Eklund, Philip Jose Farmer, Bruce Gillespie (SF Commentary), Graham Hall, Phil Harbottle, Sam Moskowitz (Helios, New Fandom), E.C. Tubbs, and Donald Wollheim (The Phantagraph), 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.