Although Judith Merril is best known for her short fiction and her novels (in collaboration with C. M. Kornbluth), she wrote a great deal of nonfiction. She wrote about SF fandom. She wrote about space and space exploration. And she wrote about science fiction. This volume collects Merrils nonfiction from The Magazine of Fantasy and Science Fiction, Extrapolation, and her Years Best anthologies. In these collected pieces, Merril works through and develops her definition of S-F and what makes S-F good. She chronicles changes within the genre, including the emergence of the New Wave. And she provides a history of the genre: its writers, its publishers, and its magazines.