The theory of a soul of the world (ψυχὴ τοῦ κόσμου, anima mundi) is almost as ancient as European philosophy itself. As far as is known, Plato conceived of it first in Timaios 34 b 3–37 c 5 (but he returned to it also in Book 10 of the Laws, 896 d 10–898 c 8). The doctrine of the world soul – not endorsed by Aristotle except perhaps indirectly by implication of his theory of the active intellect (cf. De anima Γ 5, 430 a 10–25, etc.) – then received great philosophical emphasis in the Stoic and neo-Platonic schools, which essentially transformed it according to their respective metaphysical intuitions. In order to understand, more distinctly, the philosophical content of the concept of a soul of the world, we begin our enquiry with a brief presentation and analysis of Plato’s and, respectively, Plotinus’ concepts of the world soul. This will also help us see the specificity of the early modern concept of the Weltseele.