Carl Sagan practiced no specific religion. He was raised in a Jewish family and later became known as an atheist, but he rejected that label. According to his widow, Ann Druyan, he self-identified as an agnostic.
A conflict is sometimes perceived between religion and science, but throughout his career, Sagan sought to downplay it. He instead warned against a "rigid skepticism" that denies the existence of God without evidence. The only evidence against the existence of God, he said, would be evidence of an infinitely old universe. He did not view science as necessarily a rejection of spirituality or religion.