This lecture introduces the study of domestic architecture as a key site for architectural experimentation and innovation in the modern world. It explains how houses, though small in scale, serve as testing grounds for new spatial concepts, materials, and design ideas, reflecting cultural values, technological progress, and changing social lifestyles. The lecture discusses how influential architects used houses to explore new architectural principles such as Adolf Loos’s Raumplan concept, Frank Lloyd Wright’s Prairie houses and open plans, and early International Style experiments. Through examples like Steiner House, Villa Müller, and Robie House, the lecture demonstrates how modern domestic architecture redefined spatial organization, interior–exterior relationships, and the functional arrangement of living spaces, shaping later architectural developments across larger building typologies.