The three stories presented here were written specially for this book. They are the outcome of an unusual sort of literary challenge.Arthur C. Clarke, one of the world's best-known science-fiction authors, whose works include the novel Childhood's End and the screenplay for Stanley Kubrick's motion picture 2001: A Space Odyssey, was asked to write a brief essay setting forth a general theme for a science-fiction story. Clarke's theme then was offered to Robert Silverberg, Roger Zelazny, and James Blish, three award-winning science-fiction writers; each was told to use it as the basis for a short novel, and each was given no hint of the approaches the others were taking.The result is a trio of stories that differ markedly in style, technique, and tone, while demonstrating in three individual ways the uncomfortable possibilities that the future may hold for us.