The precautionary principle is a regulatory tool that has received much attention among policy makers, industry and academics. The purpose of this paper is to shed further light on this regulatory tool. I start the paper by focusing on the question what is the precautionary principle, and how its use by policy makers has changed significantly from the 1970s to the present time. The second part of the paper examines why the precautionary principle is so controversial, examining in particular the use of it in terms of trade. The third section analyses why the precautionary principle has grown in popularity, and here I touch on, among other issues, the lack of public trust in science, its promotion by the NGOs and its application as a tool for trade protectionism. In the final section of the paper I discuss whether the precautionary principle, particularly in the European context, is here to stay. I conclude, that the use of the precautionary principle will be with the Europeans only through the medium term, as arguably it appears that the EU is following a US regulator path, albeit with a 30 year time lag.