Ouroboros is a symbol used in ancient cultures around the world. It consists of a snake biting its own tail, forming a circle, and like other circular motifs, it can symbolize unity or the cyclical nature of many aspects of life. Ouroboros is present in the cultures of ancient China, ancient Egypt, and the Americas, as well as in certain cultures of Europe and West Africa. Plato described the ouroboros as the first living creature on Earth. Sometimes, ouroboros is depicted as a dragon instead of a snake.

Though the symbol of ouroboros is widespread, its meaning is not universal. Sometimes, it is meant to symbolize the joining of opposites, similar to the yin-yang; suggestive that opposites not only coexist but are also related in a cyclical manner. In this context, ouroboros is sometimes depicted as half light and half dark. It was also used as the symbol for alchemy in the Middle Ages, as the goal of the practice was to join the conscious with the unconscious mind.

Ouroboros may be a symbol of eternity, infinity, and even resurrection, like many ring symbols. Conversely, it may be a symbol of the confines of this world. When it was adopted into some regional sects of Christianity, ouroboros was used in this latter sense. It came to suggest a separation between the world, inside the circle, and infinite divinity without. The "self-devouring" nature of ouroboros likewise became interpreted as negative, as self-destructive and transitory rather than infinite. Whereas in earlier interpretations, the cyclicality of ouroboros was a disinterested observation about the nature of the world, in Christianity, it became more of a limited "vicious circle" which could only be broken through spirituality.

Ouroboros is a mysterious symbol that many people find compelling, even if its meaning is open to interpretation. It is often used in popular culture as a generic symbol of the occult, most often in the science fiction and fantasy genres. Fascination with the ouroboros also seems to transcend culture and religion, since it was such a widespread symbol in the ancient world. Much of this fascination seems to stem from the symbol's ability to represent many different things to different people.