不二论（梵文：Advaita Vedānta，天城文：अद्वैत वेदान्त，IPA：/əd̪vait̪ə veːd̪ɑːnt̪ə/）是印度哲学中最为突出的韦丹塔，吠檀多（Vedanta）字面意思是吠陀（Veda）的终极结论，也就是吠陀经典（Veda）的最后结论。 Advaita，字面解非二元或不二，是一种一元思想体系。Advaita主要指自我（Atman）和梵（Brahman）是绝对一和同（one and the same）；另一个主要的术语Advitiya，意思是除了梵之外没有任何是一切事物）。第一个有系统整理不二论的而且著作还依然广泛流传的是商卡尔，旧译商羯罗。

Advaita Vedanta is a school of Hindu philosophy and religious practice, and one of the classic Indian paths to spiritual realization. Advaita (Sanskrit; not-two, "no second") refers to the idea that the true Self, Atman, is the same as the highest Reality, Brahman. It gives "a unifying interpretation of the whole body of Upanishads", providing scriptural authority for the postulation of the nonduality of Atman and Brahman. Followers seek liberation/release by acquiring vidyā (knowledge) of the identity of Atman and Brahman. It emphasizes Jivanmukta, the idea that moksha (freedom, liberation) is achievable in this life.