Approaches based around complexity theory are increasingly being used in the study of organisations and the delivery of services. This is the first book to explore the application of complexity theory to difficult practice issues in criminal justice and social work and is intended to stimulate debate. It brings together experts in this emerging field to address complexity theory from a range of perspectives (positivist, realist, and constructivist), providing a detailed but accessible discussion of the key issues to whole systems approaches. The chapters cover theory and research on the nature of complex adaptive systems, their application to key areas of service delivery and the efficacy and ethics of criminal justice and social work interventions. The book argues for the usefulness of applying complexity theory to address significant and intractable social problems and also challenges the reductionist approaches to solving those problems currently favoured by policy makers. It will be of interest to academics and postgraduate students in social work and criminal justice.