In more primitive religions (forms of animism and spiritism), the soul is often conceived as controlling both motor and mental processes; death, the cessation of these processes, is thus viewed as caused by the departure of the soul. Pantheism denies the individuation of human souls, and materialism declares the soul nonexistent. One of the widespread concepts in religion is that of immortality, which almost always postulates the existence of a soul that lives apart from the body after death.

In early Hebrew thought, soul connoted the life principle, but in later times the concept of a soul independent of the body arose. The soul of the righteous was seen as achieving immortality, rejoining the resurrected body at the end of days. Similarly, in Islam, a person's soul is, according to the Qur'an, the original spirit that God breathed into Adam. Its seat is the heart and it is endowed with two basic impulses—good and evil. After death the souls of the pious stay near Allah and will be reunited with their risen bodies on the Day of Judgment.

In Eastern religions, which do not stress individual salvation, the emphasis is placed on transcendent principles embodied in a multiplicity of gods (see world soul). The Hindu and Buddhist doctrines of reincarnation do not posit the existence of an individual soul, but rather stress the closeness of the human person, in successive transformations, to an overriding principle of virtue, piety, and peace.

No distinction between the rational soul (i.e., the soul of a person in scholastic Christianity) and others is made in many systems; such a distinction is quite impossible in most forms of reincarnation and of transmigration of souls. The soul of humanity when such is conceived as existing is called the world soul, or anima mundi. For many Western philosophers the term soul is synonymous with mind (e.g., René Descartes). Others, although asserting its undefinability, have seen it as a useful element in a system of ethics (e.g., Immanuel Kant). This undefinability has led yet others to reject the idea of a soul and to postulate ethical systems based upon a different conception of human nature (e.g., William James).

In Christianity the soul is all important. However, because the Bible does not give a formal definition of the concept, Christian interpretations vary greatly. Under the influence of the Neoplatonists, the soul often came to be set over against the body in a dualistic concept that posited a God-given soul distinct from an inferior, earth-bound body. Scholasticism (specifically that of St. Thomas Aquinas) studied the soul in great elaboration, and the scholastic definition of the soul as "substantial form of the body" obviates many philosophical difficulties. The nature of humanity is involved in the whole consideration of the soul; hence the term "rational soul" for the distinctive soul of humans. The soul of beasts is called the "animal soul" and that of plants the "vegetative soul." The scholastics considered the rational soul alone as immortal and capable of union with God.

The origin of the soul has been a controversial question in Christian history. Two points of view may be distinguished: creationism, which posits that God creates each individual soul in a special act of creation (at the time of conception according to some or that of birth according to others), and traducianism, which suggests that the parents in begetting the child beget the soul too. The creationist principle has been generally held sway in Christianity.