The mental plane, or world of thought, in Hermeticism, Theosophical, Rosicrucian, Aurobindonian, and New Age thought refers to the macrocosmic or universal plane or reality that is made up purely of thought or mindstuff. In contrast to Western secular modernist and post-modern thought, in occult and esoteric cosmology, thoughts and consciousness are not just a byproduct of brain functioning, but have their own objective and universal reality quite independent of the physical. This reality itself constitutes only one gradation in a whole series of planes of existence (the total number of planes varies, although seven is a common number in Theosophical formulations). In most such cosmologies and explanations of reality, the Mental Plane is located between, and hence is intermediate between, the astral plane below and the higher spiritual realms of existence above.

In esoteric cosmology, a plane other than the physical plane is conceived as a subtle state of consciousness that transcends the known physical universe.