The Viking mission has profoundly influenced scientific thinking about the question of life on Mars. Based on the results obtained from a number of Viking investigations, it is clear that the surface of the planet is too hostile to support a carbon-based biota. While the existence of biological oases elsewhere on the planet have been proposed, none have yet been found. Other information based on Viking data has focused on the possibility that life may have been present on Mars in the distant past, and Viking images have revealed sites on Mars where further exploratory studies for extinct biology are warranted. ¿ 1998 American Geophysical Union