The Upanishads are a collection of sacred texts that form one of the foundations of Hindu religious thought. The most important of these texts, written between about 600 and 300 B.C., deal primarily with the nature of humans and the universe. Originally passed on orally, these works were eventually collected and written down by wise men called rishis.

The texts of the Upanishads are said to hold the "hidden meanings" of the religious practices and ideas presented in the Vedas, an older collection of sacred texts. Hindu beliefs based on the Upanishads are known as the Vedanta, which means that they came after the Vedas.

Rather than focusing on religious ritualceremony that follows a set pattern and practice, the Upanishads are philosophical works that explore the nature of reality and meaning of life. One of their central...