The process of devolution in Wales has catalysed major political, cultural, social and institutional change. While these changes have been reflected within the research agendas of academics working within a number of disciplines, the study of criminal justice in Wales remains something of an exception. This research is an attempt to try and address this lacuna. The research charts the emergence of Wales as a distinct criminological space within the once ‘uniform’ system of England and Wales. This is explained as a consequence of the intersection of devolution in Wales with changes to the UK Government’s approach to criminal justice in England and Wales. The research shows that the unique constitutional arrangements that exist in Wales have led to the emergence of a hybrid system: criminal justice policy space occupied by two different governments, each with its own democratic mandate, policy vision and priorities. Having explained the emergence of the hybrid system in Wales, the research goes on to examine a number of key issues that emerge into clearer focus when Wales is taken seriously as a unit of criminological analysis. As such the thesis contributes towards wider criminological debates at the level of policy, practice and theory. These findings also help to develop a more critical understanding of Wales’ hybrid system. The research shows that the very structure of the hybrid system creates a situation in which UK Government criminal justice policies undermine the Welsh Government’s attempts to fulfil its responsibilities or fully implement its own policy objectives. The arguments presented throughout this research challenge the discipline of criminology to take account of the impacts of devolution on the ostensibly non-devolved criminal justice system in Wales. They also contribute towards a better understanding of debates now taking place over the possible devolution of criminal justice functions to Wales.