Berkley Medallion, cover code F975, 1964. Third [not stated] printing. The paperback reprints 10 of the 32 stories appearing in the original 1950 hardcover. STORIES: Desertion [City] (1944) by Clifford D. Simak; Mewhu's Jet (1946) novelette by Theodore Sturgeon; Nobody Saw the Ship (1950) by Murray Leinster; The Wings of Night (1942) by Lester del Rey; Arena (1944) novelette by Fredric Brown; The Roger Bacon Formula (1929) by Fletcher Pratt; Forever and the Earth (1950) by Ray Bradbury; The Miniature (1949) by John D. MacDonald; Sanity (1944) by Fritz Leiber; The Only Thing We Learn (1949) by C. M. Kornbluth.
Used availability for Groff Conklin's The Big Book of Science Fiction
1950 : Hardback
1964 : USA Mass Market Paperback