Q: What are the primary texts of Advaita Vedanta?
A: There are three primary texts of Advaita Vedanta. Together they form what is called the prasthana traya, the “three means” or “three foundations/pillars” of Vedanta.
The first primary text is actually a group of texts called the Upanishads. In turn, the revelations of the Upanishads form the basis of the other two primary Vedanta texts, The Brahma Sutras and the Bhagavad Gita. The Brahma Sutras are an attempt to systematize the teachings of the Upanishads and harmonize their internal inconsistencies. The Bhagavad Gita takes the essential teachings of the Upanishads and puts them into a story form that is easier for people to relate to and learn from.
A note: There are many Upanishads but the ten most commonly cited by Vedanta are: Aitreya, Brihadaranyaka, Chandogya, Isa, Kena, Katha, Mandukya, Mundaka, Prashna and Taittiriya. These are considered to be the mukhya (primary) Upanishads because they were commented on by Shankaracharya, Advaita Vedanta’s greatest teacher. Shankara also supposedly commented on the Svetasvatara Upanishad but because the style of this commentary differs from his commentaries on the ten other Upanishads (as well as the style of his commentaries on the Bhagavad Gita and Brahma Sutras) it is widely believed to be spurious. Some, however, claim that the Svetasvatara commentary was originally an authentic work of Shankara but was later heavily re-worked by other authors to arrive at its present form. As such, it’s still thought of as a useful tool for teaching Vedanta. But it’s not considered to be a reliable guide to Shankara’s interpretation of Vedanta.
Another significant Upanishad, despite not being commented upon by Shankara, is the Kaivalya Upanishad.
Hope that helps – Vishnu