This survey lecture course considers how theory activates new ways of making and imagining the built environment. Each week highlights a topic of architectural theory (e.g., Form, Site) and maps its development across historical periods, geographies, and fields of knowledge. Complementing the main lectures are presentations of recent projects by design faculty from the Yale School of Architecture and beyond. By challenging the familiar binary of theory versus practice, the course explores the past, present, and future limits of architectural knowledge. Moreover, by emphasizing the activating properties of theory, we will speculate on how the discipline’s toolkit of ideas and practices might engage the urgent crises of our contemporary world.