In religion and philosophy, the soul is the immaterial aspect or essence of a living being. It is typically believed to be immortal and to exist apart from the material world. Anthropologists and psychologists have found that most humans believe in the existence of a soul or spirit, and that they have cross-culturally distinguished between soul (or spirit) and body.

Different religions conceptualize souls in different ways. Buddhism generally teaches the non-existence of a permanent self (anattā), contrasting with Christianity's belief in an eternal soul that experiences death as a transition to God's presence in heaven. Hinduism views the Ātman ('self', 'essence') as identical to Brahman in some traditions, while Islam uses two terms—rūḥ and nafs—to distinguish between the divine spirit and a personal disposition. Jainism considers the soul (jīva) to be an eternal but changing form until liberation, while Judaism employs multiple terms such as nefesh and neshamah to refer to the soul. Sikhism regards the soul as part of God (Waheguru), Shamanism often embraces soul dualism with "body souls" and "free souls", while Taoism recognizes dual soul types (Hun and po).

The soul has been a central area of interest in philosophy since ancient times. Socrates envisioned the soul to possess a rational faculty, its practice being man's most godlike activity. Plato believed the soul to be the person's real self, an immaterial and immortal dweller of our lives that continues and thinks even after death. Aristotle sketched out the soul as the "first actuality" of a naturally organized body—form and matter arrangement allowing natural beings to aspire to full actualization.

Medieval philosophers expanded upon these classical foundations. Ibn Sina distinguished between the soul and the spirit, arguing that the soul's immortality follows from its nature rather than serving as a purpose to fulfill. Following Aristotelian principles, Thomas Aquinas understood the soul as the first actuality of the living body but maintained that it could exist without a body since it has operations independent of corporeal organs. In modern philosophy, the three main theories that describe the relationship between the soul and the body are interactionism, parallelism, and epiphenomenalism. During the Age of Enlightenment, Immanuel Kant defined the soul as the "I" in the most technical sense, holding that we can prove that "all properties and actions of the soul cannot be recognized from materiality".