When NASA’s Mars Pathfinder landed on the Red Planet in 1997, it released a rover that monitored the landscape, recorded weather conditions, and broadcast pictures of the surface to Earth. Presently, there is no official date or funding for a human mission to Mars, but the knowledge gained from the Pathfinder and other missions would contribute to plans for eventual human exploration of the planet. Before astronauts can take the first steps on Mars, however, much research needs to be done to guide mission planners and hardware designers. A new report from the National Academies’ National Research Council outlines the environmental, chemical, and biological hazards that NASA needs to assess before sending a human mission to Mars.