In 'Privacy, data protection and law enforcement. Opacity of the individual and transparency of power' De Hert and Gutwirth take up the challenge to rethink notions as privacy, data protection and law enforcement against the background of a theoretical analysis of the principles of the democratic constitutional state, a review of privacy and data protection legislation and a focus upon the case-law of the European Court of Human Rights in Strasbourg. The trigger of their reflection is twofold. On the one hand the authors acknowledge that privacy has come increasingly under pressure, not only as a result of the large scale introduction of information technologies and monitoring techniques, but also as a result of the far reaching public security policies that were significantly boosted during already proverbial aftermath of September 11. On the other hand they deplore the dominant confusion around notions such as privacy and data protection, focussing upon the necessity to distinguish between them, not only for analytical purposes but also and mainly for policy reasons. As privacy and data protection play important roles in balancing the powers of law enforcement and criminal investigation bodies, the authors contend that their findings will also illuminate this field. De Hert and Gutwirth show that the development of the democratic constitutional state has led to the invention of two complementary sorts of (constitutional) legal tool, namely opacity tools and transparency tools. Proceeding by the prohibition of certain kinds of conduct, opacity tools tend to guarantee non-interference in individual matters by the state and private actors. As such, they are closely linked to the recognition of human rights and a sphere of individual autonomy and self-determination. They entail the anonymity of behaviour. What is essential to opacity tools is their normative nature. Through these tools, the (constitutional) legislator takes the place of the individual as the prime arbiter of desirable or undesirable acts that infringe on liberty, autonomy and identity-building. Transparency tools, on the other hand, are meant to compel government and private actors to 'good practices' by focusing on the transparency of governmental or private decision-making and action, which is indeed the primary condition for a responsible form of governance. They define the principles by which the state and private actors must organise their conduct in relation to citizens. In other words, transparency tools tend to make the powerful transparent and accountable: they allow us 'to watch the watchdogs'.