Tactical Urbanism aims at making big changes with small scale interventions. In the same way DIY Architecture tries to improve the behaviour of the people belonging to a place, with projects that are often small and temporary. These two approaches are developed with the help of locals in the public spaces of their cities. Sometimes these projects are directly built by the designers and inhabitants themselves. The word "tactical" and the expression "do it yourself" highlight that the distance between citizens, architects and the final project is shorter in these practices, then what usually happens in orthodox architecture. DIY Architecture and Tactical Urbanism are in rapid evolution and they are used more and more for solving problems in North American and European cities. In these processes the operative dimension of the architects changes: they are closer to people and to the project. These two approches, the transformation of cities and this new dimension of the "architect" are the main focus of this book.