There are more than 200 Upanishads that have been recorded from oral traditions and passed down over centuries. Thirteen of these include core philosophical teachings of Hinduism. The philosophical concepts contained in the Upanishads are principal to Hinduism, but some are shared with Buddhism and Jainism as well.
The texts govern and explain the idea of Self-realization, which can require the practice of yoga and meditation. They also cite the concepts of non-violence, compassion, charity, and self-restraint as ethical characteristics. Many people translate the texts subjectively, which contributes to the varied Hindu schools of philosophy and religious practice. It also contributes, in part, to the various schools of yoga.