Claims of Martian life continue to spur scientific debate; this partisan account summarizes the arguments to date. DiGregorio, who has written for Omni and Discover, makes it clear that he strongly believes Mars to be the home of (at the very least) bacterial life forms. When several experiments conducted by the 1976 Viking Mars Landers returned positive results regarding signs of life, NASA scientists dismissed them as false positives. According to DiGregorio, this was based on nothing more than a refusal to accept the possibility of life beyond Earth. To bolster this argument, he surveys the history of the idea that life might exist on other planets, invoking such names as Giordano Bruno and Galileo. As our understanding of both biology and astronomy grew, the notion that life is not unique to Earth took hold in the minds of many scientists. The recent rise of the new science of exobiology opened doors to an understanding of how life might have arisen on any planet with the right conditions. But when NASA dismissed the Viking experiments, the image of Mars as a dead planet became even more firmly established--despite what DiGregorio sees as strong evidence to the contrary. The discovery in 1996 of apparent fossil life in a meteorite believed to be a fragment of Martian rock brought the entire issue back to the fore, although many researchers now claim that the new evidence is still inconclusive. Levin and Straat, who designed and built one of the Viking experiments, contribute two chapters summarizing the current status of this fascinating debate. While he is clearly a true believer, DiGregorio has an excellent grasp of his material and presents technical information clearly. Unfortunately, his organization is somewhat disjointed and he often omits background information that the lay reader might need to follow his argument.