This book presents a theory with the ambition of both describing and explaining the nature of social-work practice. It is the first book that presents an explanative theory developed specifically from and for social-work practice. One of the fundamental questions is: How can we explain how results in social-work practice emanate from social worker’s and clients’ actions under certain contextual conditions?The theory presented in this book is named CAIMeR, which means that it takes a systematic and coherent approach to the theory of Contexts, Actors, Interventions, Mechanisms and Results. The meta-theoretical basis is critical realism, where a key feature is the concept of generative mechanisms. This perspective can help us capture the often unobservable powers that explain how results in social work emerge as a consequence of interventions and contextual conditions. The book also presents a domain theory that explains how social workers’ professional practice is conditioned by politics, management and institutional conditions. This book is essential reading for students in social work and adjoining disciplines, but also for researchers, managers and professional social workers.