The point about complexity is that it is useful – it helps us to understand the things we are trying to understand. (Byrne, 1998, p 7)

This book is about challenge, stimulation and intellectual inquiry; in it, we provide a range of examples from criminal justice, social work and other public systems settings, which are written by people who have extensive experience, both academic and practice-based. We argue that these examples (and they are not exhaustive) demonstrate the importance of understanding the necessity of whole-systems approaches based upon understandings of non-linearity. Most of us in our daily lives, both personal and professional, realise that despite our best efforts, things do not always work out in the way that we planned, sometimes with minor consequences and sometimes with dire consequences. Furthermore, these consequences can sometimes become locked into patterns and regularities that appear difficult to change despite best efforts and outside interventions. These consequences can become evident in criminal justice and social work in relation to reoffending, addiction and child protection for example, with similar problems and mistakes seeming to repeat themselves. It is our contention that interdisciplinary approaches based upon the study of complexity theory and non-linearity helps us both to understand and to act in just and ethical ways to respond to these problems.

The study of non-linear dynamical systems (NDS) through the development of chaos and complexity theory has become increasingly influential in both the physical and social sciences, having been proclaimed as the third revolution in human thinking after relativity and quantum mechanics. The NDS approach views the world as comprising a series of interacting systems and subsystems, where change in any part of those systems or their subsystems can change the context for all of the other elements. Increasingly, approaches based around ideas of complexity theory are being used in the study of organisations and the delivery of services, social work, psychology, medicine, and mental health and addiction studies. Importantly, complexity theory addresses issues of self organisation, evolution and emergence within whole systems and fractal (nested system) relationships. The interrelated nature of these systems can work from the genetic and cellular foundations of life through to the ‘whole systems’ of individuals, society and the state, thus having profound implications for our understanding of cause and effect.