Lynn Margulis, Distinguished Professor in the Department of Geosciences at the University of Massachusetts at Amherst, has been a member of the National Academy of Sciences since 1983. She has been described by E. O. Wilson as 'one of the most successful synthetic thinkers in modern biology'. She is best known for her pathbreaking work on the bacterial origins of cell organelles and for her collaboration with James Lovelock on Gaia theory. Her previous books include Symbiosis in Cell Evolution; Five Kingdoms (with K. V. Schwartz); and (with Dorian Sagan) The Origins of Sex, The Garden of Microbial Delights, What is Life?, What is Sex?, and Slanted Truths: Essays on Gaia, Symbiosis and Evolution. Less