From the fire altar to the self
The Upaniṣads are the latest layer of the Vedic literature. The oldest of them, such as the Bṛhadāraṇyaka and the Chāndogya, are usually dated to roughly the 8th to 5th centuries BCE. They take the form of dialogues between teachers and students, kings and priests, husbands and wives.
Their great question is what lies at the heart of a person and of the universe. Many passages answer that the inner self, ātman, is ultimately one with brahman, the ground of all that exists, and that to know this truly is to be free.
Karma, rebirth and release
The Upaniṣads are also among the earliest Indian texts to set out ideas that became central to Indian religion: that beings are reborn again and again, that what they do (karma) shapes what they become, and that there is a final release from the cycle.
These ideas were not yet universal. Other groups in northern India held them too, in different forms, and scholars disagree about where they first arose.
A conversation the Buddha joined
The Buddha shared the language of karma, rebirth and liberation, but he refused to identify anything in experience as a permanent self. Many scholars read his teaching of not-self (anattā) as, in part, a direct reply to the kind of thinking found in the Upaniṣads.
Why it matters
Many of the great philosophical questions later addressed by Buddhism were already being fiercely debated.
History and tradition
What historians can say
The dating of the early Upaniṣads is approximate and disputed, and it is not certain that all of the oldest ones were composed before the Buddha. Some scholars, notably Johannes Bronkhorst, argue that karma and rebirth came from the culture of 'Greater Magadha' in the east rather than from the Vedic tradition itself.