Some architectural transformations are modest, some are revolutionary. Shining a light on the hidden side of the accepted narrative of the history of architecture, this book explores works which transform existing buildings to build a way forward, through adaptations, additions and visual shifts. Examining 30 buildings across Europe, North America and South America, spanning from the early Middle Ages to the end of the 20th century, it demonstrates the creative possibilities of working with existing buildings. The book reveals how formal inventions can shape architecture and our environment over time in a built world constantly in a state of becoming. As we face a climate emergency, it taps into our deep cultural knowledge about the inventive use and re-use of buildings. Generously illustrated with architectural plans and over 300 colour images, it provides an alternative to the dominant view which sees conservation and preservation of historic buildings as a 20th century creation.