Urban re-activation is becoming an increasingly relevant and complex topic in Europe, as it brings together a growing community of influential actors who, in recent years, have established a number of successful interventions in the field of re-use and re-appropriation. In this book, we will not only investigate these informal practices as they pertain to architects, but also to various groups and collectives, designers, entrepreneurs, programmers, geographers, and so on-concerned citizens who have already begun to transform their ideas into actions by introducing new models and innovative ideas. Following this initial introduction, we shall present a series of interviews from a selection of experts, researchers, local administrators, and architects, all active in the re-activation of urban spaces throughout the European Union, whose realization of innovative new projects and initiatives will play a central role in our discussions over urban re-activation, and, in our view, represents some of the most interesting examples that define our toolbox for re-use. These valuable contributions, consisting of various keywords, models, and examples representing a broad range of European experiences, are intended to help the reader in identifying and understanding some of the most powerful and innovative tools for urban re-activation.