Since 1 January 2005, citizens in the Netherlands are obliged to show their ID if a police officer asks them to. The (extended) identification duty is meant to prevent crimes and to improve the enforcement of the law. Bart van Klink (Tilburg University) and Nicolle Zeegers (University of Groningen) have investigated how the identification duty is enforced in legal practice by interviewing 12 police officers in 4 different cities and looking at statistical data on enforcement. According to most of the police officers interviewed the identification duty helps to remove anonymity from citizens, which may keep them from committing crimes (in particular crimes in groups, e.g., hooligans). Moreover, the identification duty appears to be instrumental in normalizing citizens: by asking for an ID, police officers are able to discourage behaviour that conflicts with some (legal or moral) standard of normality. This small-scale empirical research indicates that police officers stress the law’s preventive effect. Although prevention may be a valuable goal, it may also constitute a pretext for far-reaching intrusions on citizens’ freedom. An important normative question is how to prevent the police from using this legal instrument too actively for the sake of prevention.