Provides a comprehensive account of the recent `Spirit' and `Opportunity' Mars Exploration Rover missions. Relates how NASA/ESA have sought evidence of life on Mars, with the prevailing mood sometimes being optimistic and sometimes pessimistic. Details an account of the rationale for the tests for life carried out by the Viking missions in 1976, with an account of the debate over their results. A concise primer for readers wishing to `bone up' when NASA next sends a lander explicitly to seek life on Mars. Discusses the nature of life on Mars in terms of the most primitive forms of life on Earth, and reviews the implications of there being life on both planets.