This document provides a summary of the history of architectural theory from antiquity to the present. It begins with Vitruvius in the 1st century BCE and his work "De Architectura", which defined classical orders and proposed the Vitruvian triad of firmness, commodity, and delight. During the Renaissance, thinkers like Alberti built upon Vitruvius. The Enlightenment saw renewed interest in classical architecture. In the 19th century, theorists like Pugin and Ruskin reacted against neoclassicism. Modernism in the 20th century was shaped by thinkers like Sullivan, the International Style architects, and Wright. Contemporary theory grapples with issues of globalization, technology, and the digital realm.