Yajnavalkya or Yagyavalkya (याज्ञवल्क्य, ) is a Hindu Vedic sage figuring in the Brihadaranyaka Upanishad (c. 700 BCE). Yajnavalkya proposes and debates metaphysical questions about the nature of existence, consciousness and impermanence, and expounds the epistemic doctrine of neti neti ("not this, not this") to discover the universal Self and Ātman. Texts attributed to him include the Yajnavalkya Smriti, Yoga Yajnavalkya and some texts of the Vedanta school. He is also mentioned in various Brahmanas and Aranyakas.
The Brihadaranyaka Upanishad is dated at c. 700 BCE,. Staal notes that though the name Yajnavalkya is derived from yajna, which connotes ritual, Yajnavalkya is referred to as "a thinker, not a ritualist".
Yājñavalkya was the pupil of Uddālaka Āruṇi, whom he defeated in debate.
In the Brihadaranyaka Upanishad, a set of dialogues portrays Yajnavalkya as having two wives, one Maitreyi who challenges Yajnavalkya with philosophical questions like a scholarly wife; the other Katyayani who is silent but mentioned as a housewife. While Yajnavalkya and Katyayani lived in contented domesticity, Maitreyi studied metaphysics and engaged in theological dialogues with her husband in addition to "making self-inquiries of introspection". In contrast to the Brihadaranyaka Upanishad, the epic Mahabharata states Maitreyi is a young beauty who is an Advaita scholar but never marries.
The figure of Yajnavalkya is considered by Scharfstein as one of the earliest philosophers in recorded history. Yajnavalkya is credited by Witzel for coining the term Advaita (non-duality of Atman and Brahman). The ideas attributed to him for renunciation of worldly attachments have been important to Hindu sannyasa traditions.
Yajnavalkya is associated with several other major ancient texts in Sanskrit, namely the Shukla Yajurveda, the Shatapatha Brahmana, the Brihadaranyaka Upanishad, the Dharmasastra named Yājñavalkya Smṛti, Vriddha Yajnavalkya, and Brihad Yajnavalkya. He is also mentioned in the Mahabharata and the Puranas, as well as in ancient Jainism texts such as the Isibhasiyaim.