The concept of the anima mundi (Latin), world soul (Ancient Greek: ψυχὴ κόσμου, psychḕ kósmou), or soul of the world (ψυχὴ τοῦ κόσμου, psychḕ toû kósmou) posits an intrinsic connection between all living beings, suggesting that the world is animated by a soul much like the human body. Rooted in ancient Greek and Roman philosophy, the idea holds that the world soul infuses the cosmos with life and intelligence. This notion has been influential across various systems of thought, including Stoicism, Gnosticism, Neoplatonism, and Hermeticism, shaping metaphysical and cosmological frameworks throughout history.

In ancient philosophy, Plato's dialogue Timaeus introduces the universe as a living creature endowed with a soul and reason, constructed by the demiurge according to a rational pattern expressed through mathematical principles. Plato describes the world soul as a mixture of sameness and difference, forming a unified, harmonious entity that permeates the cosmos. This soul animates the universe, ensuring its rational structure and function according to a divine plan, with the motions of the seven classical planets reflecting the deep connection between mathematics and reality in Platonic thought.

Stoicism and Gnosticism are two significant philosophical systems that elaborated on this concept. Stoicism, founded by Zeno of Citium in the early 3rd century BCE, posited that the universe is a single, living entity permeated by the divine rational principle known as the logos, which organizes and animates the cosmos, functioning as its soul. Gnosticism, emerging in the early centuries of the Common Era, often associates the world soul with Sophia, who embodies divine wisdom and the descent into the material world. Gnostics believed that esoteric knowledge could transcend the material world and reunite with the divine.

Neoplatonism and Hermeticism also incorporated the concept of the world soul into their cosmologies. Neoplatonism, flourishing in the 3rd century CE through philosophers like Plotinus and Proclus, proposed a hierarchical structure of existence with the World Soul acting as an intermediary between the intelligible realm and the material world, animating and organizing the cosmos. Hermeticism, based on writings attributed to Hermes Trismegistus, views the world soul as a vital force uniting the cosmos. Hermetic texts describe the cosmos as a living being imbued with a divine spirit, emphasizing the unity and interconnection of all things. Aligning oneself with the world soul is seen as a path to spiritual enlightenment and union with the divine, a belief that experienced a resurgence during the Renaissance when Hermeticism was revived and integrated into Renaissance thought, influencing various intellectual and spiritual movements of the time.

Plato described the universe as a living being in his dialogue Timaeus (30b–d):

Thus, then, in accordance with the likely account, we must declare that this Cosmos has verily come into existence as a Living Creature endowed with soul and reason [...] a Living Creature, one and visible, containing within itself all the living creatures which are by nature akin to itself.

Plato's Timaeus describes this living cosmos as being built by the demiurge, constructed to be self-identical and intelligible to reason, according to a rational pattern expressed in mathematical principles and Pythagorean ratios describing the structure of the cosmos, and particularly the motions of the seven classical planets. The living universe is also a god titled Ouranos and Kosmos, which shows, as scholars have argued, that Plato mediates between the poetic and presocratic traditions.

In Timaeus, Plato presents the cosmos as a single, living organism that possesses a soul and intelligence. The demiurge, a divine craftsman, creates the universe by imposing order on pre-existing chaotic matter. This creation is not ex nihilo but rather a process of organizing the cosmos according to the eternal Forms, which are perfect, immutable archetypes of all things.