The cosmology of J. R. R. Tolkien's legendarium combines aspects of Christian theology and metaphysics with pre-modern cosmological concepts in the flat Earth paradigm, along with the modern spherical Earth view of the Solar System.

The created world, Eä, includes the planet Arda, corresponding to the Earth. It is created flat, with the dwelling of the godlike Valar at its centre. When this is marred by the evil Vala Melkor, the world is reshaped, losing its perfect symmetry, and the Valar move to Valinor, but the Elves can still sail there from Middle-earth. When Men try to go there, hoping for immortality, Valinor and its continent of Aman are removed from Arda, which is reshaped as a round world. Scholars have compared the implied cosmology with that of Tolkien's religion, Roman Catholicism, and of Medieval poetry such as Pearl or Dante's Paradiso, where there are three parts, Earth, Purgatory or the Earthly Paradise, and Heaven or the Celestial Paradise. Scholars have debated the nature of evil in Middle-earth, arguing whether it is the absence of good – the Boethian position, or equally as powerful as good – the Manichaean view.