The third in a series of superb science fiction. The Alpha series of anthologies center on no particular theme except that of literary quality. Two criteria were used in the selecting of these stories-literary merit and importance to the genre. The result is that the variety of subjects is matched only by the richness and diversity of their handling-brilliant, frightening, clever, bizarre, powerful, witty, funny-and several steps in-between. Simply put, here is the best science fiction from the best science fiction writers. The main intent of the Alpha series is to assemble groups of stories that give pleasure by demonstrating the richness and variety of the science-fiction form. Quality of storytelling is the touchstone; I make no effort to gather the stories in any one volume according to any thematic pattern. Yet thematic patterns seem to creep into the books like insidious invaders from far galaxies. The first Alpha contained a cluster of tales dealing with travel through time-relativity gone topsy-turvy all over the book. The second volume, through no prior intent of the editor, seemed to deal almost entirely with the tensions arising out of man's confrontation with technology. And in this third one, I find, a prevailing theme in nearly every story is the conflict between ourselves and strangers. Again and again, through some odd accident of balance, you will find tales of tense encounters, showing protagonists facing the unknown quantities of time and space. Freud tells us that nothing ever happens by accident. Perhaps so. These anthologies are not assembled in a random process, and no doubt the editor's mind serves as a thematic filter in ways that are not clear to the editor himself except in hindsight. And one can reasonably object that virtually every good science-fiction story deals in meetings with the unknown, so that the supposed theme detected here is no true theme at all, but only a universal characteristic of the genre. In any event, here are ten outstanding stories. I think they achieve what is for me the basic science-fiction accomplishment: they show the reader visions he has not previously had, and send him away transformed and enlarged. Go thou and read. Go and be changed.