The Upanishads are late Vedic and post-Vedic Sanskrit texts that "document the transition from the archaic ritualism of the Veda into new religious ideas and institutions" and the emergence of the central religious concepts of Hinduism. They are the most recent addition to the Vedas, the oldest scriptures of Hinduism, and deal with meditation, philosophy, consciousness, and ontological knowledge. Earlier parts of the Vedas dealt with mantras, benedictions, rituals, ceremonies, and sacrifices.

Sanskrit is a classical language belonging to the Indo-Aryan branch of the Indo-European languages. It arose in South Asia after its predecessor languages had diffused there from the northwest in the late Bronze Age. Sanskrit is the sacred language of Hinduism, the language of classical Hindu philosophy, and of historical texts of Buddhism and Jainism. It was a link language in ancient and medieval South Asia, and upon transmission of Hindu and Buddhist culture to Southeast Asia, East Asia and Central Asia in the early medieval era, it became a language of religion and high culture, and of the political elites in some of these regions. As a result, Sanskrit had a lasting effect on the languages of South Asia, Southeast Asia and East Asia, especially in their formal and learned vocabularies.