Precautionary ReasoningEvery day we make decisions involving risks, benefits, and precautions. We engage in what I call precautionary reasoning in a variety of decision-making contexts, including lifestyle choices (e.g. smoking tobacco, riding motorcycles, eating excessively), financial decisions (e.g. investing money, loaning money, purchasing goods), health care choices (e.g. seeking medical treatment, taking preventative measures), and public policy decisions (e.g. approving drugs, developing new technologies, enacting environmental or public health protections). Precautionary decisions range from the mundane (e.g. whether to take an umbrella to work) to the profound (e.g. whether to permit human genome editing), and they may impact anywhere from a few people to the entire world.Since the mid-twentieth century, philosophers, economists, psychologists, political scientists, and legal theorists have written a great deal about the ethical, legal, and policy issues related to assessing and managing risks. In the book, I will develop a comprehensive framework for thinking about risks that draws insights from different scientific and humanistic disciplines and has applications for environmental and public health policy. The framework will help us gain a better understanding of precautionary reasoning in general as well as a form of precautionary reasoning known as the precautionary principle (PP).