The Upanishads are a collection of ancient Sanskrit texts that form the philosophical backbone of Hinduism. Composed between 800 BCE and 500 BCE, they are considered the end part of the Vedas, the oldest sacred texts of Hinduism. The Upanishads primarily explore the concepts of Brahman (the ultimate reality) and Atman (the inner self), delving deep into the nature of existence, the universe, and the relationship between the individual soul and the universal spirit. These texts mark a significant transition from ritualistic practices to philosophical inquiry and spiritual understanding in Indian religious thought. The Upanishads are philosophical dialogues that address the nature of reality, the essence of life, and the path to enlightenment. They reject materialism and emphasize the pursuit of spiritual wisdom and the understanding of one's connection to the eternal, unchanging truth. The teachings in the Upanishads have profoundly influenced various aspects of Indian philosophy, spirituality, and culture. They are considered by many to be amongst the greatest contributions to world philosophy and spiritual literature.