The doctrine of the serpent seed, also known as the dual-seed or the two-seedline doctrine, is a controversial and fringe Christian religious belief which explains the biblical account of the fall of man by stating that the Serpent mated with Eve in the Garden of Eden, and the offspring of their union was Cain. This event resulted in the creation of two races of people: the wicked descendants of the Serpent who were destined for damnation, and the righteous descendants of Adam who were destined to have eternal life. The doctrine frames human history as a conflict between these two races in which the descendants of Adam will eventually triumph over the descendants of the Serpent.

The curse of Cain and the mark of Cain are phrases that originated in the story of Cain and Abel in the Book of Genesis. In the stories, if someone harmed Cain, the damage would come back sevenfold. Some interpretations view this as a physical mark, whereas other interpretations see the "mark" as a sign, and not as a physical mark on Cain himself. The King James Version of the Bible reads "set a mark upon Cain".