Since the beginning of the U.S. space program, the National Aeronautics and Space Administration (NASA) has trained astronauts in basic earth science topics to support their observations of Earth's surface from low Earth orbit. From its roots in the Apollo geology training campaigns, we describe the evolution of astronaut Earth observation training across human spaceflight programs, with a focus on the training for space shuttle and International Space Station (ISS) missions. Astronauts' Earth observation experiences—both preflight training and interactions with scientists on the ground during spaceflight missions—provide relevant information for defining training requirements for future astronaut exploration missions on other planetary surfaces.