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. At that time it assumed its final identity, Speculation.
Contributors to Speculation include Brian Aldiss, Greg Benford, John Boston, John Brosnan (Big Scab), Ken Bulmer (Science Fantasy News), F.M. Busby (Cry of the Nameless), John Foyster, Richard Gordon, Tim Hildebrand, Lang Jones, David Masson, Archie Mercer (Vector), Beryl Mercer (Link, Oz), Michael Moorcock (Typo, A Fanzine Named Eustace), Larry Niven, Andy Offut, Alexei Panshin, John J. Pierce, writing on Cordwainer Smith, Martin Pitt, Charles Platt (Beyond), Chris Priest, Bob Rickard, and Ben Solon.
Issue 25 featured a cover by Richard Bergeron (Warhoon). Artwork was contributed by Jim Cawthorn and Vincent DiFate, among others.
Speculation also featured an interview with writer J.G. Ballard.
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.