The Mercury 13 were thirteen American women who took part in a privately funded research program run by NASA physician William Randolph Lovelace II in 1959-1960, which aimed to test and screen women for spaceflight. The first participant, pilot Geraldyn "Jerrie" Cobb helped Lovelace identify and recruit the others. The participants successfully underwent the same physiological screening tests as had the astronauts selected by NASA for Project Mercury. While Lovelace called the project Woman in Space Program, the thirteen women decades later became known as the "Mercury 13"— a term coined in 1995 as a comparison to the Mercury Seven astronauts. The Mercury 13 women were not allowed in NASA's official astronaut program, and at the time, never trained as a group, nor flew in space.

William Randolph Lovelace II was an American physician who made contributions to aerospace medicine.