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, John Boston, John Brosnan, Ken Bulmer, F.M. Busby (Cry of the Nameless), John Foyster, Richard Gordon, Lang Jones, David Masson, Archie Mercer, Beryl Mercer (Link), Michael Moorcock (Ergo Ego), Larry Niven, Alexei Panshin, John J. Pierce, writing on Cordwainer Smith, Martin Pitt, Chris Priest, and Bob Rickard, Ben Solon.
Artwork was contributed by Jim Cawthorn.
Speculation also featured and interview with writer J.G. Ballard.
Letters of comment included Ivor Latto.
A series of "Speculation Conferences" were also organised, adopting a similarly "sercon" approach to science fiction analysis. It won the very first Nova Award, in 1973.