Given the obsession with information and secrecy in today’s world, it can be difficult to imagine a time when governments held few secrets and worried little about what information was public knowledge. In Restricted Data: The History of Nuclear Secrecy in the United States (University of Chicago Press, 2021), Alex Wellerstein chronicles how much of this change can be traced to the development of atomic weapons in the 1940s and the efforts both then and since to restrict the details about them. Secrecy was a factor in nuclear technology from the start, as scientists argued amongst themselves about the need for self-censorship about the possibility of atomic weapons. By the start of the Manhattan Project the United States government had assumed responsibility for maintaining secrets, which they often did in ways that frustrated the scientists involved. What was hoped to be a temporary restriction because of the war became permanent with the onset of the Cold War, as the government fought to restrict any knowledge which they thought might aid the Soviet Union in the construction of nuclear weapons. While this effort came under attack from an increasingly aggressive group of anti-secrecy activists in the post-Watergate era, the government identified new threats in the post-Cold War era that justified the need to maintain nuclear secrets down to the present day.