This thesis investigates how different forms of uncertainty emerge in the context of environmental risk research and risk policy (risk-based planning), and how such incertainties affect the outcome of risk analysis and management when conceived of as an interaction between science and policy. The thesis further aims at exploring how certain meta-scientific imperatives influence the way uncertinties and ultimately risks are understood and created. In so doing, the analysis makes use of the concept of institutional uncertainty to depict a state of several intervening forms of uncertainty, relating to information, cognition/value-based and (inter)organizational sources.