What do scientists know about the possibility of life outside our solar system? How does Catholic science fiction imagine such worlds? What are the implications for Catholic thought? This collection brings together leading scientists, philosophers, theologians, and science fiction authors in the Catholic tradition to examine these issues. In the first section, Christian scientists detail the latest scientific findings regarding the possibility of life on exoplanets. The second part brings together leading Catholic science fiction authors who describe how “alien” life forms have been prevalent in the Catholic imagination from the Middle Ages right up to the present day. In the final section, Catholic philosophers and theologians examine the implications of discovering intelligent life elsewhere in the universe. Rather than worrying that the discovery of intelligent extraterrestrials might threaten the dignity of humans or their existence, the contributors here maintain that such creatures should be welcomed as fellow creatures of God and potential subjects of divine salvation.