On July 20, 1969, Neil Armstrong took one small step and made history. Over the course of the next three-and-a-half years, twelve lunar explorers, including Alan Shepard and Gene Cernan, touched down on the moon's surface. Author and engineer Suzanne Slade reveals how the Apollo missions (1969-1972) built upon one another and led to important discoveries about our nearest neighbor in space. Back matter includes an afterword by Alan Bean (1932-2018), the fourth person to walk on the moon.