Peter Abelard (12 February 1079 – 21 April 1142) was a medieval French scholastic philosopher, leading logician, theologian, teacher, musician, composer, and poet.

In philosophy he is celebrated for his logical solution to the problem of universals via nominalism and conceptualism and his pioneering of intent in ethics. Often referred to as the "Descartes of the twelfth century", he is considered a forerunner of Rousseau, Kant, and Spinoza. He is sometimes credited as a chief forerunner of modern empiricism.

In Catholic theology, he is best known for his development of the concept of limbo, and his introduction of the moral influence theory of atonement. He is considered (alongside Augustine) to be the most significant forerunner of the modern self-reflective autobiographer. He paved the way and set the tone for later epistolary novels and celebrity tell-alls with his publicly distributed letter, The History of My Calamities, and public correspondence.

In history and popular culture he is best known for his passionate, tragic love affair and intense philosophical exchange with his brilliant student and eventual wife, Héloïse d'Argenteuil.

Abelard is considered one of the founders of the secular university and pre-Renaissance secular philosophical thought.

Abelard argued for conceptualism in the theory of universals. (A universal is a quality or property which every individual member of a class of things must possess if the same word is to apply to all the things in that class. Blueness, for example, is a universal property possessed by all blue objects.) According to Abelard scholar David Luscombe, "Abelard logically elaborated an independent philosophy of language...[in which] he stressed that language itself is not able to demonstrate the truth of things (res) that lie in the domain of physics."

Writing with the influence of his wife Heloise, he stressed the subjective intention as determining, if not the moral character, at least the moral value, of human action. With his wife, he is the first significant philosopher of the Middle Ages to push for this interpretation before Thomas Aquinas.

He helped establish the philosophical authority of Aristotle, which became firmly established in the half-century after his death. It was at this time that Aristotle's Organon first became available, and gradually all of Aristotle's other surviving works. Before this, the works of Plato formed the basis of support for philosophical realism.