By virtue of its ambiguity, it has largely been left to the courts to flesh out the scope and application of the precautionary principle. This paper examines the contribution made by EC courts to defining the parameters of precautionary decision making. In so doing, it illustrates that, though the precautionary principle is seen to operate in a number of regulatory contexts, discernible trends in judicial interpretations of precaution and the underlying notion of 'uncertainty' can nevertheless be identified. In contrast with early judgments, the courts are beginning to explicitly interpret risk assessment processes as having a pivotal role in determining precautionary intervention. Rather than finding simply that circumstances of uncertainty warrant precautionary measures, the courts have started to require that clear, or 'concrete', evidence of harm, deriving from risk assessment, is established before intervention is justified. This paper posits three explanations for this shift: (i) the 'better regulation' initiative within Europe; (ii) the Commission's Communication on the Precautionary Principle; and (iii) WTO litigation on precautionary safeguard measures. The judicial move to affiliate precaution with risk assessment processes in decision making can be seen as a reflection of these factors.