An "Upanisad" is a teaching session with a guru, and the thirteen texts of the "Principal Upanisads"--which comprise this volume--form a series of philosophical discourses between teacher and student that question the inner meaning of the world. Composed beginning around the eighth century BCE, the Upanisads have been central to the development of Hinduism, exploring its central doctrines: rebirth, karma, overcoming death, and achieving detachment, equilibrium, and spiritual bliss. Speaking to the reader in direct, unadorned prose or lucid verse, the Upanisads collected here embody humanity's...