J. Baird Callicott is Distinguished Research Professor Emeritus at the University of North Texas and co-editor-in-chief of the Encyclopedia of Environmental Ethics and Philosophy. Callicott has served the International Society for Environmental Ethics as President and Yale University as Bioethicist-in-Residence. He is the leading contemporary exponent of Aldo Leopold’s land ethic and has elaborated an Earth ethic, Thinking Like a Planet, in response to climate change. His most recent book is Greek Natural Philosophy: The Presocratics and their Importance for Environmental Philosophy.