Twenty-five years ago, on July 20, 1976, NASA’s Viking 1 lander soft-landed on the surface of Mars, becoming the first successful mission to land on the red planet, as well as the first successful American landing on another planet. With a second lander later joining the first on the surface and with two orbiters circling the planet, the Viking project changed our understanding of that alien world. Its treasure trove of images and data covering the entire Martian globe remains a valuable scientific resource for the study of Mars.