Martian biology is likely alive and well on the red planet, but tucked away in caves or dwelling underground, sustained by pockets of water. That prospect has spurred scientists to look for exotic life forms here on Earth, far from the maddening crowd of topside biota that covers our planet. This quizzical quarry for life is helping devise the strategies, the tools, and the procedures for unearthing the biological leftovers from an ancient Mars, or hardy microbes that might exist on that distant world today. Experts on the search for underground Martian biology took part in the Sixth International Mars Society Conference, held August 14-17, 2003.