Anne Conway was an extraordinary figure in a remarkable age. Her Principles of the Most Ancient and Modern Philosophy is the most interesting and original philosophical work written by a woman in the seventeenth century. Her radical and unorthodox ideas are important not only because they anticipated the more tolerant, ecumenical, and optimistic philosophy of the Enlightenment, but also because of their influence on Leibniz. This newly translated and fully annotated edition includes an introduction that places Conway in her historical and philosophical contexts, together with a chronology of her life and a bibliography.