Various parties relate to the precautionary principle with various understandings, claims and hopes. One of the ways to comprehend this multiplicity of meanings is to examine the composition of this problematic norm in the societal and institutional settings where it occurs. In this paper, I address its elaboration on the European Union institutional terrain with the European Commission's Communication on the Precautionary Principle. This effectuation of the precautionary principle embraces a number of issues of transnational or multilevel governance, expertise, legitimacy and sovereignty. The crucial matter that this paper engages in initially is that of risk analysis, the procedural framework that the precautionary principle confronts with its innovative articulations of science and policy-making, but to which I argue that it succumbs in part. Also explored, in turn, are further framings of the precautionary principle: science versus policy, a given policy domain-environment-in relation to others, as well as action versus inaction (whereas I argue that the precautionary principle ought to be about acting and doubting). These are further evaluated in the conclusions, together with the predicament of establishing a common understanding or defining the precautionary principle. I show that, complementary to drivers of divergence, one finds support for a common approach, though there is no radial symmetry in these tangled stakes, and any 'diffusion' of the precautionary principle has to be actively carried out for a shared understanding to be more widely shared. In this process, Europe, the European Commission, its Communication, and the precautionary principle are being shaped into diverse compositions of unity in diversity.