BACKGROUND: The Upanishads, a collection of Indian sacred texts, have grown over centuries; some have even been added in modern times. The earliest ones, however, include many of the fundamental principles of Hinduism. They also influenced the development of Buddhism and other faiths. The excerpt here lays out some of the basic ideas of karma and reincarnation, linking people’s conduct and desires in their current life to the fate of their soul in the future.