[3][4] In the mid-1940s, Moskowitz founded the Eastern Science Fiction Association (ESFA), a science-fiction fandom organization based in Newark, New Jersey which held conventions.

His exhaustive cataloging of early sf magazine stories by important genre authors remains the best resource for nonspecialists.

Theodore Sturgeon, although noting the book's many imperfections, praised Explorers of the Infinite, saying "no one has surveyed the roots of SF as well as Mr. M.; probably no one ever will; prossibly [sic], no one else can.

Moskowitz wrote it in a bombastic style that made the events he described seem so important that, as fan historian Harry Warner Jr. quipped, "If read directly after a history of World War II, it does not seem like an anticlimax.

"[8][9] Floyd C. Gale wrote in his review of the book that "[f]ortunately, most of these petulant warriors have since grown up—but their historian is still leading their ghostly legions that are more real than today to him.

"[11] Moskowitz was also renowned as a science fiction book collector, with a tremendous number of important early works and rarities.