For the past century and a half, writers of what we have learned to call "science fiction" have been trying to create a modern conscience for the human race. In the same period many writers in the field have produced trivial, ephemeral works of "popular" fiction. The premise upon which this book is based is that a sufficient number of works of genuine merit have been produced in this field to justify its study as an aspect of modern literature, as well as an important feature of contemporary culture.--From foreword.