Dharmadhatu (Sanskrit: धर्मधातु|Dharmadhātu|Realm of Ultimate Reality; ;) is the 'dimension', 'realm' or 'sphere' (dhātu) of the Dharma or Absolute Reality.
In Mahayana Buddhism, dharmadhatu means "realm of all phenomena", "realm of all things" (the entire universe with all visible and invisible things) or "realm of eternal truth". It is referred to by several analogous terms from Mahayana Buddhist philosophy, such as Tathata (Reality "as-it-is"), emptiness, dependent co-arising and eternal Buddha. It is the "deepest nature, or essence".
Dharmadhatu is the purified mind in its natural state, free of obscurations. It is the essence-quality or primal nature of mind, the fundamental ground of consciousness of the trikaya, which is accessed via the mindstream.
When the buddha-nature has been realised, dharmadhatu is also referred to as the Dharmakāya, the Body of Dharma Truth.
It is associated with supreme cosmic buddha Vairocana.
Kang-nam Oh traces the origin of dharmadhatu to the Avatamsaka Sutra. It has been further developed by the Hua-yen school:
The Śrīmālādevī Sūtra (3rd century CE), also named The Lion's Roar of Queen Srimala, centers on the teaching of the tathagatagarbha as "ultimate soteriological principle". It states that the tathagata-garbha is the "embryo" of the Dharmadhatu and the Dharmakaya:
In the Śrīmālādevī Sūtra, there are two possible states for the Tathagatagarbha: