The 'Precautionary Principle'-allowing or favoring regulation of risks despite uncertainty - has been at the center of debates about European and U.S. risk management since the 1990s. Does adopting the precautionary principle protect us against uncertain risks, or does it inhibit progress and introduce new risks? Has Europe become 'more precautionary' than the United States? The Reality of Precaution is the first study to go beyond the rhetoric of precaution as an abstract principle and test the reality of precaution in practice. Challenging conventional wisdom about European and U.S. approaches to risk regulation, this groundbreaking resource finds that since the 1970s there has been little transatlantic difference in the overall level of precaution, but that instead there have been variations in precaution across particular individual risks. For example, while Europe has been more precautionary regarding genetically modified foods, beef hormones, toxic chemicals, and climate change, the U.S. has been more precautionary regarding mad cow disease, air pollution, ozone depletion, and terrorism. Moreover, both the U.S. and Europe have adopted systems of regulatory oversight through impact assessment.Combining a dozen case studies, a quantitative analysis of almost 3,000 risks, and cross-cutting chapters on politics, law, and risk perceptions, this book argues that the relationship between U.S. and European regulatory approaches is best understood not as conflict or competition, nor in terms of divergence or reversal, but rather as a process of selective application of precaution to particular risks, and a continuing exchange of ideas yielding mutual cooperation and hybridization. The Reality of Precaution advises policymakers in both the U.S. and Europe to compare actual regulatory experience, to borrow useful policy designs, and to seek optimal (not maximal) precaution that accounts fully for risks, costs, and ancillary impacts.