In the prevailing literature on police systems and their associated traditions of democratic control, continuity is deemed to be a much stronger characteristic than change. This study calls that insight into question. It examines and compares the changes that have occurred in the police systems of Belgium, Denmark, England & Wales, Germany and the Netherlands in the last few decades. These countries are geographic neighbours, and their police systems have undergone signifi cant reforms in recent years. Why these changes have taken place is the central question of this study, which was conducted by an international team of researchers. A police system is understood as the organisational structure of the civil regular police. It is the framework that makes possible the governance, organisation, implementation by and control of the police. Frameworks defi ne the boundaries of police operations and can make possible or exclude certain solutions for juridical or political reasons. They potentially offer opportunities for change, adaptation, and innovation. In conjunction with the way police work is carried out in practice, a police system determines how adequately the police operate and to what extent they can cope with changing societal challenges. Complexity is a hallmark of modern police systems in terms of their organisation, management and control, not only on paper but also in practice. The changes to police systems in the countries studied show similarities as well as development in divergent directions. The study highlights the infl uences of community policing, continuing and increasing professionalisation and specialisation, and a predominance of New Public Management insights. In all fi ve countries centralisation and localism manifest themselves simultaneously. On the other hand police systems bear the imprint of existing politico-administrative and judicial structures and culture, existing institutionalised power structures and power relations, and the history of policing and the police system. They are often related to broader changes at issue in the public sector in the country. The occurrence of crises can cause divergence from existing patterns of development. What thepolice do, how they work and perform, and how they are governed and controlled appear to be loosely interdependent.