Antoine Arnauld and Pierre Nicole were philosophers and theologians associated with Port-Royal Abbey, a center of the Catholic Jansenist movement in seventeenth-century France. Their enormously influential Logic or the Art of Thinking, which went through five editions in their lifetimes, treats topics in logic, language, theory of knowledge and metaphysics, and also articulates the response of heretical Jansenist Catholicism to orthodox Catholic and Protestant views on grace, free will and the sacraments. This edition presents a new translation of the text, together with a historical introduction and suggestions for further reading.