In the 1970s, microbiologist Lynn Margulis and atmospheric chemist James Lovelock developed the Gaia theory. Embracing the circular logic of life and engineering systems, the Gaia theory states that Earth is a self-regulating complex system in which life interacts with and eventually becomes its own environment. Gaia describes a living Earth: a body in the form of a planet. Fusing science, mathematics, philosophy, ecology and mythology, *Gaia and Philosophy*, with a new introduction by Dorion Sagan, challenges Western anthropocentrism to propose a symbiotic planet. In its striking philosophical conclusion, the revolutionary Gaia paradigm holds important implications not only for understanding life's past but for shaping its future.