Among the most challenging aspects of making decisions is dealing with the inherent uncertainties. There are uncertainties in how to frame or approach the issue under consideration, as well as lack of information due to relevant areas not being investigated or because available methods are limited. Furthermore, some things are just unknowable and sometimes we are not aware of what we do not know. These are the aspects that the DPMP 'uncertainty project' is tackling, as outlined below. Not surprisingly, numerous ways have been developed to understand and deal with uncertainty. What is surprising is that there has been relatively little exchange between or synthesis of these different approaches. This project is a step in fostering such interaction and integration. It responds to growing recognition that uncertainty cuts across disciplinary and practice boundaries and that we need to trade ideas and experiences to develop better tactics and methods for conceptualising and coping with uncertainty. Exposure to current debates and competing perspectives will highlight unresolved issues and stimulate new understanding and approaches. The overall aim is to improve available methods for dealing with uncertainty, especially in relation to illicit drugs policy, although this research will also have a broad-reaching impact. The objective is to allow us to be better equipped to deal with the different dimensions of uncertainty. The most obvious uncertainty that DPMP confronts is lack of data about a whole range of aspects of illicit drug use. While there are standard ways of dealing with this, such as estimation