After Second World War public and political decision makers wished to correct the apparent negative consequences of science and technology. This resulted in a call for ethical responsibility in science and technology and a new generation of environmental regimes aimed at controlling or managing the consequences of human interaction with the environment. The claim of this paper is that the Precautionary Principle can be understood as a combination of these trends. The Precautionary Principle is presented and discussed in detail. In (...) particular it is specified a) when the Principle is to be used, b) what measures follow from the decision to use it, and c) who is to be consulted in democratic decisions of the use of the Principle. (shrink)