Aristotelianism (/ˌærɪstəˈtiːliənɪzəm/ ARR-i-stə-TEE-lee-ə-niz-əm) is a philosophical tradition inspired by the work of Aristotle, usually characterized by deductive logic and an analytic inductive method in the study of natural philosophy and metaphysics. It covers the treatment of the social sciences under a system of natural law. It answers why-questions by a scheme of four causes, including purpose or teleology, and emphasizes virtue ethics. Aristotle and his school wrote tractates on physics, biology, metaphysics, logic, ethics, aesthetics, poetry, theatre, music, rhetoric, psychology, linguistics, economics, politics, and government. Any school of thought that takes one of Aristotle's distinctive positions as its starting point can be considered "Aristotelian" in the widest sense. This means that different Aristotelian theories (e.g. in ethics or in ontology) may not have much in common as far as their actual content is concerned besides their shared reference to Aristotle.

In Aristotle's time, philosophy included natural philosophy, which preceded the advent of modern science during the Scientific Revolution. The works of Aristotle were initially defended by the members of the Peripatetic school and later on by the Neoplatonists, who produced many commentaries on Aristotle's writings. In the Islamic Golden Age, Avicenna and Averroes translated the works of Aristotle into Arabic and under them, along with philosophers such as Al-Kindi and Al-Farabi, Aristotelianism became a major part of early Islamic philosophy.

Moses Maimonides adopted Aristotelianism from the Islamic scholars and based his Guide for the Perplexed on it and that became the basis of Jewish scholastic philosophy. Although some of Aristotle's logical works were known to western Europe, it was not until the Latin translations of the 12th century and the rise of scholasticism that the works of Aristotle and his Arabic commentators became widely available. Scholars such as Albertus Magnus and Thomas Aquinas interpreted and systematized Aristotle's works in accordance with Catholic theology.

After retreating under criticism from modern natural philosophers, the distinctively Aristotelian idea of teleology was transmitted through Wolff and Kant to Hegel, who applied it to history as a totality. However, this project was criticized by Trendelenburg and Brentano as non-Aristotelian, Hegel's influence is now often said to be responsible for an important Aristotelian influence upon Marx.

Recent Aristotelian ethical and "practical" philosophy, such as that of Gadamer and McDowell, is often premised upon a rejection of Aristotelianism's traditional metaphysical or theoretical philosophy. From this viewpoint, the early modern tradition of political republicanism, which views the res publica, public sphere or state as constituted by its citizens' virtuous activity, can appear thoroughly Aristotelian.

Alasdair MacIntyre was a notable modern Aristotelian philosopher who helped to revive virtue ethics in his book After Virtue. MacIntyre revises Aristotelianism with the argument that the highest temporal goods, which are internal to human beings, are actualized through participation in social practices.

The original followers of Aristotle were the members of the Peripatetic school. The most prominent members of the school after Aristotle were Theophrastus and Strato of Lampsacus, who both continued Aristotle's researches. During the Roman era, the school concentrated on preserving and defending his work. The most important figure in this regard was Alexander of Aphrodisias who commentated on Aristotle's writings. With the rise of Neoplatonism in the 3rd century, Peripateticism as an independent philosophy came to an end. Still, the Neoplatonists sought to incorporate Aristotle's philosophy within their own system and produced many commentaries on Aristotle.

Byzantine Aristotelianism emerged in the Byzantine Empire in the two decades after 1118 through the initiative of the princess Anna Comnena who commissioned a number of scholars to write commentaries on previously neglected works of Aristotle. Michael of Ephesus wrote commentaries on the works of Aristotle's animal biology, on the Sophistical Refutations, the only work of the Organon not to have a commentary and the Politics, completing the series of commentaries on Aristotle's extant works. Byzantine philosophers also filled in the gaps in the commentaries that had survived down to their time; Alexander of Aphrodisias' commentary on the Metaphysics, of which only the first five books survived, was completed by Michael of Ephesus, who, along with Eustratius, compiled a number of fragmentary commentaries on the Nicomachean Ethics which they supplemented with their own interpretations.