Scholars date the start of the “Anthropocene” period, during which human activity began to have substantial effects on the environment, variously from the beginning of human farming roughly 8,000 years ago to the emergence of industrialism in the 19th century. But all agree that the advent of nuclear weapons and power has dramatically changed the potential for environmental alterations. This article, published in American History, details how our ongoing attempts to harness the benefits of the atomic age while lessening its negative impacts will need to confront the substantial environmental and public-health issues that have plagued nuclear technology since its inception.