In less than a decade, six robotic spacecraft, one lander, two rovers, and three orbiters have explored the atmosphere, surface, and interior of the planet Mars. Among the highlights of over 40 years of Mars exploration are the Mars Exploration Rovers, conducting extremely successful investigations of sites postulated to have been covered by liquid water long ago. Spirit and Opportunity have returned data that point to a past very different from the cold, arid Martian landscape that we see today. Building upon these and earlier findings, NASA is returning to the planet with the recently launched Mars Reconnaissance Orbiter. In 2007, a lander will examine subsurface ice in the northern polar region, and in 2009 a large rover carrying a payload of laboratory instruments will search for ancient habitable environments. This lecture focuses on our emerging understanding of Mars and NASA strategies for future exploration.