Étienne Henri Gilson (1884-1978) was a French philosopher and historian of medieval philosophy, best known for his studies of Thomas Aquinas, his account of the relationship between Christian faith and Greek philosophy, and his role in the twentieth-century revival of Thomistic and scholastic thought. He held chairs at the Sorbonne and the Collège de France, co-founded the Pontifical Institute of Mediaeval Studies in Toronto, and was elected to the Académie française in 1946. Gilson's central historiographical claim - that medieval philosophy constitutes a distinct and philosophically serious tradition rather than a mere theological interlude between antiquity and modernity - remains contested among historians of philosophy, as does his related thesis of “Christian philosophy.”

Gilson's scholarly output centered on detailed textual studies of Aquinas, Bonaventure, Duns Scotus, Augustine, and Descartes, alongside synthetic works such as The Spirit of Mediaeval Philosophy and The Unity of Philosophical Experience. He is often situated within the twentieth-century Thomistic revival that traces its institutional roots to Pope Leo XIII's 1879 encyclical Aeterni Patris, and he is widely credited as one of the principal figures - alongside Jacques Maritain - in the movement known as Neo-Scholasticism or Neo-Thomism.

Gilson argued that medieval thinkers, working under the pressure of reconciling biblical revelation with Greek philosophical categories, produced genuine philosophical innovations - notably a metaphysics of existence (the real distinction between essence and existence) that he considered absent from, or undeveloped in, classical Greek thought. He termed this body of thought “Christian philosophy,” a label and a thesis that generated sustained debate among historians and philosophers, most notably in the famous 1931 Société française de philosophie session where Gilson defended the concept against critics including Émile Bréhier. Specialists continue to disagree about whether Gilson's reading of figures like Aquinas was historically accurate or colored by his own philosophical commitments, and about whether “Christian philosophy” names a coherent category at all. For the longer narrative of his career, training under figures such as Lucien Lévy-Bruhl, and his institutional work, see etienne-gilson-history.

• Gilsonian Thomist viewpoint: Holds that Gilson's historical reconstruction of Aquinas is substantially correct and that his “Christian philosophy” thesis identifies a real and philosophically significant development, particularly Aquinas's metaphysics of esse. See etienne-gilson-christian-philosophy-thomist-viewpoint.
• Skeptical historiographical viewpoint: Holds that Gilson's account imposes a retrospective philosophical unity (often Thomist-inflected) onto a more disparate and internally conflicted medieval tradition, and that “Christian philosophy” is a theological category mistaken for a historical one. See etienne-gilson-historiography-skeptical-viewpoint.
• Analytic medievalist viewpoint: Holds that Gilson's narrative-historical approach, while valuable as intellectual history, should be supplemented or superseded by close analytic reconstruction of medieval arguments on their own logical terms, independent of Gilson's broader theological framing. See etienne-gilson-analytic-medievalism-viewpoint.
• Secular rationalist viewpoint: Holds that the notion of “Christian philosophy” is internally incoherent, since philosophy by definition proceeds by reason alone and cannot be qualified by a confessional adjective without ceasing to be philosophy. See etienne-gilson-christian-philosophy-secular-viewpoint.

• The 1931 Société française de philosophie debate over whether “Christian philosophy” is a legitimate historical and philosophical category, pitting Gilson against Bréhier and others. See etienne-gilson-christian-philosophy-1931-controversy.

• History of Étienne Gilson's career and influence
• Debate: Does "Christian philosophy" name a coherent category?
• Debate: Is Gilson's reading of Aquinas on essence and existence accurate?
• Scholasticism
• Aeterni Patris
• Thomas Aquinas
• Jacques Maritain

• Gilson, Étienne. The Spirit of Mediaeval Philosophy. Translated by A. H. C. Downes. New York: Charles Scribner's Sons, 1936.
• Gilson, Étienne. The Unity of Philosophical Experience. New York: Charles Scribner's Sons, 1937.
• Gilson, Étienne. History of Christian Philosophy in the Middle Ages. New York: Random House, 1955.
• Shook, Laurence K. Étienne Gilson. Toronto: Pontifical Institute of Mediaeval Studies, 1984.
• Hittinger, F. Russell. “Christian Philosophy: Three Forms.” The Cambridge Companion to Christian Philosophy, edited by Charles Taliaferro and Chad Meister, 173-186. Cambridge: Cambridge University Press, 2010.
• O'Meara, Thomas F. “Gilson, Étienne.” New Catholic Encyclopedia, 2nd ed., vol. 6, 234-236. Detroit: Gale, 2003.