After conflicts with Ace head Donald A. Wollheim, he worked as a freelancer. He edited an original story anthology series called "Universe", and a popular series of "The Best Science Fiction of the Year" anthologies that ran from 1972 until his death in 1987. He also edited numerous one-off anthologies over the same time span. He was nominated for the Hugo for Best Editor thirteen times (1973–1975, 1977–1979, 1981–1987), winning twice (1985 and 1987). His win in 1985 was the first time a freelance editor had won.