Chapter 1 delineates several forms of uncertainty (including outcome, probability, causal, and scientific uncertainty) in order to underscore the complexity of environmental harms and to illustrate how scholars of environmental policy and normative ethics have largely misconstrued what uncertainty consists of—treating it narrowly as probability uncertainty, where what is unknown is the likelihood that harm may come to pass. The notion of “genuine” uncertainty is introduced to complicate these existing conceptions and treatments of uncertainty and to preface the central charge of Chapter 1: that existing defenses of precautionary risk regulation, as well as opposing arguments supporting formal risk assessment, are incomplete and flawed. And because the central justification that proponents of precaution appeal to—specifically, our prevailing epistemic limitations—is turned on its head by critics of precaution to justify the opposite conclusion, there is only one plausible alternative to vindicate the precautionary principle: we must ground precaution in something other than what we can or cannot know about the potential for harm. After demonstrating that existing arguments in support of precautionary risk regulation do not successfully refute common objections, Chapter 1 sketches an alternative, normative justification for requiring precautionary safeguards under conditions of uncertainty—namely, that individuals have a right not to have others gamble with their welfare by putting them in potential harm’s way.