"The Space Trilogy" is a series of science fiction novels written by C.S. Lewis. The trilogy consists of three books: "Out of the Silent Planet," "Perelandra," and "That Hideous Strength." The series explores themes of theology, morality, and the clash between good and evil in the context of interplanetary travel and encounters with extraterrestrial beings. Each book follows the protagonist, Dr. Elwin Ransom, on his adventures in space and his interactions with the inhabitants of other planets.