Edited by Robert Silverberg

A Martian Odyssey, Stanley G. Weinbaum: American scientist, Dick Jarvis, part of the first international expedition to the planet Mars sets out to explore the planet on his own when his flying vehicle malfunctions, leaving him stranded miles away from the landing site. Twilight,  John W. Campbell, Jr. : Jim Bendell has an eerie experience with a strange and mysterious hitch-hiker, who introduces himself as Ares Sen Kenlin and who claims to be a time traveler from the year of 3059. Helen O'Loy,Lester Del Rey: Two young men - Dave, a mechanic and Phil, a medical student - collaborate on modifying a household robot, originally meant only to cook and clean.  But complications arise when the robot begins to develop emotions. The Roads Must Roll, Robert A. Heinlein: In the near future, roadtowns (wide rapidly-moving passenger platforms that reach speeds of 100 mph) have replaced highways and railways as the dominant transportation method in the United States. Yet this story is about much, much more than that... Microcosmic God, Theodore Sturgeon: Kidder, a highly secretive and reclusive biochemist,  gets impatient with the slow progress of innovation by humans, and develops a synthetic life form - Neoterics . They live at a greatly accelerated rate, have a very short lifespan, produce many generations over a short period of time - and are capable of producing fabulous technology - but men are greedy and want a share of the neoterics' genius... Nightfall, Isaac Asimov:  On the planet Lagash  there is no night; it is perpetually illuminated by at least one of the six suns of its multiple star system. Yet every two thousand years, civilisation undergoes a collapse on Lagash, and another such time is approaching. Scientists have discovered that the societal collapses are due to eclipses - but will this knowledge save civilisation this time?  The Weapon Shop,  A. E. van Vogt: Fara, a small business operator, faces   professional and personal troubles when -  despite his fierce devotion to the Empress who rules the solar system - a weapons shop, which sells fantastic technology but which is not controlled by the Empress, materialises in his town.  Mimsy Were the Borogoves, Lewis Padgett (Henry Kuttner and C. L. Moore): In the distant future, a posthuman scientist attempts to build a time machine, testing it by sending a box of hastily gathered educational toys into the past. When the box fails to return, he constructs another and tests it the same way, but it also fails to return. He thinks he's failed - but he would be wrong... Huddling Place,  Clifford D. Simak: In the distant future, humans live and easy life on Mars, supported by efficient and intelligent robots. Intelligent Martians co-exist with the humans on that planet...but is it really Utopia?  Arena, Fredric Brown: Amid an escalating conflict between Earth and alien Outsiders, massive armadas from both sides are set to meet in what looks to be an evenly matched battle. Bob Carson, scout ship pilot, blacks out and awakens in an arena with an alien Outsider - both have been chosen to fight to death and the loser will doom his species to extinction.  First Contact, Murray Leinster: Two space exploration ships meet - one is crewed by humans and the other by aliens. But even when communication is established, there is an impasse - neither ship can leave without ensuring that the other cannot track them to their home planet!