There is a clear and pressing need for collective action to develop alternative approaches to the way we organize our activities. This necessity implies the development of a robust theory that outlines a potential, attainable, and desirable future, which is embedded in the inherent contradictions of the present. Cultural-Historical Activity Theory represents such a strong interventionist theory.The initial section of this publication outlines the evolution of this theory, from its origins in the work of 20th-century Soviet psychologists to its more recent developments. The second part of the book provides insight into the key concepts and their application in research. The third part of this book describes the potential for intervention aimed at transforming activity systems. It also explains the methodological principles of formative intervention and the change laboratory.