Willy Ley (October 2, 1906 - June 24, 1969) was a science writer and space advocate who helped popularise rocketry and spaceflight in Germany and the United States in the early-mid twentieth century.

Ley was born in Berlin and studied to become a paleontologist. However, he developed an interest in spaceflight after reading Hermann Oberth's book Die Rakete zu den Planetenraumen ("By Rocket into Interplanetary Space"). He soon published his own book on the subject, Die Fahrt in den Weltraum ("Travel in Outer Space") in 1926.

In 1927, he became one of the first members of Germany's amateur rocket group, the Verein für Raumschiffahrt (VfR - "Spaceflight Society") and wrote extensively for its journal, Die Rakete ("The Rocket"). With Oberth, he also acted as a consultant on Fritz Lang's film Frau im Mond ("Woman in the Moon")

The VfR disbanded in 1933 amidst controversy within its membership over the interest the military was taking in their activities. Ley decided to flee the Nazi regime and went to the United States in 1935, where he became a citizen in 1944.

He continued to write extensively on spaceflight in terms that the lay person could understand. His works from the 1950s and 60s are regarded as classics of popular science and include The Conquest of Space (1950), The Conquest of the Moon (with Wernher von Braun and Fred Whipple, 1953), and Beyond the Solar System (1964). He also acted as science consultant for the Tom Corbett series of children's science fiction books and TV series.

Ley died in Jackson Heights, Queens sadly just a month before the first person set foot on the moon.