There is an inherent and inevitable tension between police powers and human rights. Adequate police powers are necessary to allow the police to fulfil their tasks; but exercise of such powers will necessarily interfere with the right of respect for private life and must therefore be proportionate to the aim to be achieved. The fundamental argument underlying this thesis is that privacy is valuable, either in its own right, or as a necessary prerequisite for sustaining more fundamental rights. Yet privacy also has costs: the greater the individual 'sphere of privacy', the narrower the scope for obta ining and utilising personal data for societal ends e.g. in this context the suppression or punishment of criminality. It is necessary, therefore, at an early stage in the thesis to undertake a contextual overview of expressions of the concept and value of privacy in Western liberal democracies. Establishing why privacy and privacy rights may be worthy of defence, both for individuals as well as for society as a whole, provides a framework for determining what must necessarily fall within the scope of privacy for that value to be realised . This thesis advocates an approach based on the identification and application of a general underlying principle of privacy and the shaping of the future evolution of the law in line with such a principle. New police information systems or new forms of personal data processing for police purposes do not emerge into an informational vacuum; on the contrary, they merge with and draw upon existing systems of data collection and processing, which are themselves evolving, e.g. computer records of people's bank transactions, their telephone calls, their activity on the Internet, their medical conditions, their education and employment histories etc. The thesis thus provides an overview of the pan-European police information systems already deployed, or planned to be deployed, with the aim of creating for the reader a cognitive map of a complex interaction of systems within which personal data is already collected, stored, shared and/or exchanged on a daily basis, exploring along the way the data protection regimes within those structures. The central themes of the thesis rest upon analysis of the influence of the CoE Recommendation R(87)15 on Regulating the Use of Personal Data in the Police Sector which provides a sector-specific application of the data protection principles established in the CoE Convention for the Protection of Individuals with regard to Automatic Processing of Personal Data. To provide the reader with context for interpreting the empirical research findings, the thesis traces the history of the drafting of Recommendation R(87}15, based on research amongst materials drawn from the CoE's archives in Strasbourg. The findings of the empirical research - resulting from analysis of responses to a questionnaire deployed to Data Protection Authorities or Ministries of Justice in all member States of the CoE, exploring the implementation or otherwise of R(87}15 in each State - provide, for the first time, in a snap-shot, a census of where European legislation stands as regards processing of personal data for police purposes, as the European Union progresses beyond the first pillar/third pillar dichotomy in the post-Lisbon Treaty era. To further inform this analysis, the questionnaire findings were supplemented by in-depth semistructured interviews with domain experts from national data protection authorities, or law enforcement authorities, in select States. ii Based on the forgoing analysis, the thesis outlines aspects of the current legal regime that should be updated or improved, primarily in the context of the reform of the EU data protection framework, with a special focus on data processing in the police and criminal justice sector. This analysis identifies the extent to which the principles of Recommendation R(87)15 have been adopted, adapted, strengthened, weakened or abandoned in the current EU reform proposals. The provisions of Recommendation R(87)15, especially those which reinforce the principles of necessity, proportionality and purpose-specification/limitation are "an inalterable necessary minimum," 1 even for police and security forces. Yet it is argued that this "necessary minimum" is too minimal, and that changed circumstances make it advisable to further strengthen and expand the provisions of Recommendation R(87)15. The thesis concludes that the central question to be asked when restrictions on a fundamental right are concerned is: "How much limitation of a fundamental right is permissible in a democratic constitutional state in which fundamental rights are a constitutive element?" As such it is a modest contribution to the big questions facing our societies regarding the kind of society we want to build, and the kind of policies we need to put in place to reach our goals.