This book is intended to examine the history of radiation protection up to the present from the perspective of regime theory, with a view to elucidating what this case teaches about how a strong regime in a controversial area can form and maintain itself. This is a particularly relevant issue at present when the overall international rules-based order is under threat and scientific authority doubted. There are significant parallels between the international radiation protection regime and efforts to slow climate change, stop the proliferation of nuclear weapons, manage the applications of artificial intelligence, control the use of drones, and confront the risks posed by pandemics. While each has its own dynamics, all these issues involve the interaction of scientific discovery and expertise with the societies that generate them. Learning what works and what does not is vital if we are to limit harm and ensure survival of humanity on a shrinking and warming planet.