Original sin, in Christian doctrine, the condition or state of sin into which each human being is born; also, the origin (i.e., the cause, or source) of this state.

Original sin, also described as ancestral sin, is a Christian view of the nature of sin in which humanity has existed since the fall of man. Original sin arose from Adam and Eve's transgression in Eden, the sin of disobedience in eating the forbidden fruit from the tree of the knowledge of good and evil.

Original sin is the guilt of disobedience to God passed on from Adam and Eve to all subsequent generations. For Catholics, original sin is a state, implying that infants are guilty at birth; for Protestants, in contrast, sin is an act, and original sin implies merely a propensity to commit sinful acts.