In June 1979, Congress passed the Espionage Act, the first act of the three secrecy-defining statutes that have shaped so much of the last hundred years of modern American secrecy doctrine. Together with two other statutes that followed in later decades-the Atomic Energy Acts of 1946 and 1954, and the Patriot Act of 2001-these three Acts picked out inflection points in the great ratcheting process that has expanded secrecy from the protection of troop positions and recruitment stations through an entire field of the physical sciences to almost the whole of government and civil society. Along with a surround of orders, directives, laws, and policies, these three Acts ground the modern world of national security secrecy. Necessarily schematic, my aim here is to follow the long term history of secrets over the last hundred years, using the debates and cases that that encircled them to understand better the governing principles of what information had to be hidden. What dangers did each period identify among things that should be secret? What were the properties and assumed power of these secrets? What kind of thing could, in the end, properly be declared secret? In short, I am interested in using the Acts to fix what it is that secrets were: An historically changing ontology of secrets from World War I through the Long War (World War II through the Cold War), and finally into the Terror Wars, our unbounded conflict.