Gregory Vlastos (Greek: Γρηγόριος Βλαστός; July 27, 1907 – October 12, 1991) was a scholar of ancient philosophy, and author of several works on Plato and Socrates. A Christian, Vlastos also wrote about Christian faith. He is considered to be "a preeminent scholar on Socrates who transformed the analysis of classical philosophy."

Vlastos was born in Istanbul, to a Scottish mother and a Greek father, where he received a Bachelor of Arts from Robert College before moving to Harvard University where he received a PhD in 1931. After teaching for several years at Queen's University in Kingston, Ontario, Canada, he moved to Cornell University in 1948. He was Stuart Professor of Philosophy at Princeton University between 1955 and 1976, and then Mills Professor of Philosophy at University of California, Berkeley until 1987. He received a MacArthur Foundation Fellowship in 1990. He was twice awarded a Guggenheim Fellowship, was a fellow of the American Academy of Arts and Sciences, a corresponding fellow of the British Academy, and a member of the American Philosophical Society.[2] Vlastos died in 1991, before finishing a new compilation of essays on Socratic philosophy.

He is credited with bringing about a renaissance of interest in Plato among philosophers throughout the world.[2] Many of Vlastos' students have become important scholars of ancient philosophy, including Terence Irwin, Richard Kraut, Paul Woodruff, and Alexander Nehamas.