Hal Clement, one of the all-time greats of science fiction, was defining hard science fiction before such distinctions were even being thought of. He once described his approach to writing: "[T]he rules must be quite simple. They are; for the reader of a science-fiction story, they consist of finding as many as possible of the author's statements or implications which conflict with the facts as science currently understands them. For the author, the rule is to make as few such slips as he possibly can." He was named a Grand Master by the Science Fiction and Fantasy Writers of America in 1999 and an annual award for Excellence in Children's Science Fiction has been established in his memory and is presented each year at the annual Worldcon. This collection presents some of his finest shorter pieces as collected by his friend and colleague, Lester del Rey.