This first of several Arbor House anthologies designed to be modern definitive volumes of SF (and fantasy and horror) followed the last volume of Silverberg's Alpha series by two years, with more than a few stories that had appeared in those volumes (13, to be precise), reappearing among the 39 stories here. Like the Alpha volumes, then, this Arbor House volume represents Silverberg's personal taste and standards for excellence in SF, as much as it does a historical assessment of the field.
Silverberg's introduction explicitly recalls the two big 1946 anthologies, Adventures in Time and Space and The Best of Science Fiction, and so he deliberately scopes this volume to include nothing written before 1946, to provide a modern supplement to those earlier standards.