This magazine was for many years the companion title to Amazing Stories, starting in the early 1950s when the "pulp" magazines were dying out, replaced by the "digest" size ones. It was almost a continuation of the pulp Amazing's companion, Fantastic Adventures - but the editorial policy was quite different, and the magazines did actually overlap.
Many of the top science fiction writers appeared here over the years, including Fritz Leiber, Robert Silverberg, Philip K. Dick, and Roger Zelazny. For some years before the end, it relied greatly on reprints, but somehow, particularly under the editorship of Ted White, it was still an important and entertaining magazine.
edit: the old picture-link had died - I wonder how well the new one will last...?
new edit: not all that long, it seems... I just hope nothing happens to PhotoBucket!