Management of water resources is afflicted with uncertainties. Nowadays it is facing more and new uncertainties since pace and dimension of changes (e.g. climatic, demographic) are accelerating and are likely to increase even more in the future. Hence it is crucial to find pragmatic ways to deal with these uncertainties in water management. This thesis argues for an analytical yet pragmatic approach to enable decision-makers to deal with uncertainties in a more explicit and systematic way and allow for better informed decisions. The approach is based on the concept of framing and mental models, referring to different ways in which people make sense of the world and of uncertainties. It is analysed how uncertainties are framed and dealt with in water management practice and strategies are elaborated how dealing with uncertainties can be improved in water management practice. The research for this thesis has been closely linked to the EU research project NeWater (New Approaches to Adaptive Water Management under Uncertainty, www.newater.uos.de) (2005-2009). It draws on practical experiences of water managers at local and regional level in river basin management in three case studies, i.e. the German Wupper, the Dutch Kromme Rijn, both sub basins of the river Rhine, and the Doñana region located in the Guadalquivir Estuary in Spain. For the assessment of framing of uncertainty two different methods were developed and applied in the three river basins. Both aim at identifying parameters of importance in the process of framing uncertainty in order to understand how uncertainties get framed. The empirical research confirmed that indeed water managers are faced with a range of uncertainties and that so far no systematic approaches are applied for dealing with those in management practice. The results in the case studies suggest that there are no universal findings as to how actors frame uncertainties but rather that framings are dependent on the respective uncertainty situation, on roles (e.g. project leader, public administration, scientist etc.), and most often on personal traits. The case study findings moreover suggest that there are no universally valid parameters of influence in the framing of uncertainties. Neither could a clear superiority of one approach over the other be discerned. Nonetheless, the parameters of framing of uncertainty proved to be a supportive tool for preparing and structuring decision-making in the case studies and developing improvement options for dealing with uncertainty. Beyond the results of the development of approaches for the assessment of framing of uncertainty in water management practice, processes of communication and learning turned out to be of major importance. Making framings of uncertainties explicit by help of parameters of framing proved to be useful in the case studies for revealing different points of views on the uncertainties and with regard to the strategies to deal with them. This is a first step in enabling dialogue among opposed framers and an important precondition for reframing and learning which is crucial for the long-term performance in management of natural resources.