Arete (Ancient Greek: ἀρετή, romanized: aretḗ) is a concept in ancient Greek thought that refers to "excellence" of any kind—especially a person or thing's "full realization of potential or inherent function." The term may also refer to excellence in "moral virtue."

The concept was also occasionally personified as a minor goddess, Arete (not to be confused with the mythological Queen Arete), who, together with sister Homonoia, formed the Praxidikai ("Exacters of Justice").

In its earliest appearance in Greek, this notion of excellence was bound up with the notion of the fulfillment of purpose or function: living up to one's potential. A person of arete is of the highest effectiveness; such a person uses all of their faculties—strength, bravery, and wit—to achieve real results. In the Homeric world, arete involves all of the abilities and potentialities available to humans. Though particularly associated with "manly" qualities, the Homeric usage of the term was not necessarily gender-specific, as Homer applied the term to both the Greek and Trojan heroes as well as major female figures, such as Penelope, the wife of Greek hero Odysseus. In the Homeric poems, arete is frequently associated with bravery, but more often with effectiveness.

In some contexts, arete is explicitly linked with human knowledge, where the expressions "virtue is knowledge" and "arete is knowledge" are used interchangeably. In this sense, the highest human potential is knowledge, and all other human abilities derive from this central capacity. If arete is knowledge, the highest human knowledge is knowledge about knowledge itself. In this light, the theoretical study of human knowledge, which Aristotle called "contemplation", is the highest human ability and happiness.

The ancient Greeks applied the term arete (ἀρετή) to anything: for example, the excellence of a chimney, the excellence of a bull for breeding, and the excellence of a man. The meaning of the word changes depending on what it describes since everything has its own excellence; the arete of a man is different from the arete of a horse. This way of thinking originates from Plato, where it can be seen in the Allegory of the Cave. In particular, the aristocratic class was presumed, essentially by definition, to be exemplary of arete:

The root of the word is the same as aristos, the word which shows superlative ability and superiority, and aristos was constantly used in the plural to denote the nobility.

By the 5th and 4th centuries BC, arete as applied to men had developed to include quieter virtues, such as dikaiosyne (justice) and sophrosyne (self-restraint). Though Plato tried to produce a moral philosophy that incorporated this new usage, it was in the Nicomachean Ethics of Aristotle that the doctrine of arete found its fullest flowering. Aristotle's Doctrine of the Mean is a paradigm example of his thinking.

Aristotle deliberated on the various goals of education: including practical skills, arete, and theory. Educating towards arete means boys would be educated towards things that are useful in life. However, there is no agreement about what constitutes arete, which leads to disagreement about how to train students for arete. To say that arete has a common definition of excellence or fulfillment may be an overstatement simply because it was very difficult to pinpoint arete, much less the proper ways to go about obtaining it.