Windows are moments in modern architecture where we look to ascertain elegance, technical expression and material language or to capture a certain atmosphere. A window opening is as much an interval and an opportunity as it is a device for admitting light, air or views; it is simultaneously a physical aperture but also a philosophical opening of collaboration and reflection. In order to understand the language of a building we might look to the detail of the window. But what does this mean and why does modern architecture invest so much expression in the window? This book explores how the act of detailing and situating windows in buildings is a key proponent in the language of architecture, which both informs and works with the contingencies of design and construction. It investigates 18 case studies in-depth using painstakingly drawn details and vivid photographs in full colour to define what makes these windows “great” and how each window is situated within both its technical and philosophical context and as an overall development of modern architecture. Case studies include the work of Walter Gropius, Mies van der Rohe, Pierre Chareau, Frank Lloyd Wright, Alvar Aalto, Carlo Scarpa, Le Corbusier, Stirling and Gowan, Raili and Reima Pietilä, Louis Kahn, Peter Womersley, Miralles/Pinós, Steven Holl, Glen Murcutt and O’Donnell + Tuomey.