Ace editor Donald A. Wollheim began this series in 1965 with co-editor Terry Carr (who would later launch the 'Ace Specials'), initially emphasizing a world-wide scope, with stories in the first volume by Joseph Nesvadba, Harry Mulisch, and Colin Free, though subsequent volumes drew material almost exclusively from genre sources. Beginning with the third volume, each story was decorated by a Jack Gaughn black and white illustration, and beginning with the fifth volume, the US Science Fiction Book Club published hardcover editions, as shown below. (The paperbacks in the photo are second printings with revised titles.) The series ended as both Wollheim and Carr left Ace, Wollheim to found DAW books, Carr to go freelance, each subsequently publishing his own best-of-year anthology series.