Editor Silverberg has chosen eight stories by noted science fiction writers all dealing with ""some of the challenges we think human explorers will face as they embark on the scientific expeditions of the day after tomorrow."" Virtually all of the stories are available elsewhere; therefore, this is strictly an additional purchase for fans who would like to know just what Ursula K. Le Guin, Murray Leinster, Clifford D. Simak, Poul Anderson, Arthur C. Clarke, Isaac Asimov, Edmond Hamilton, and of course the editor (who always seems to include one story of his own in his anthologies) think (or have thought) awaits man the explorer. Probably of them all, the ironies of Simak's ""Beachhead"" (1951) and Asimov's ""Each an Explorer"" (1956) have endured the test of time best. Acceptable, not exceptional.