Tracing the genealogy of conspiracy theory, from Machiavelli through the "paranoid style" to QAnon Truthers, birthers, flat-Earthers, the deep state, crisis actors, chemtrails, the Epstein files, Pizzagate, the Plandemic-it seems as though there's a conspiracy theory for every situation. But what exactly is a conspiracy theory? And why is the term used to describe beliefs that are so very unlike theories (at least in the scientific sense of the word)? In this erudite and original book, Andrew McKenzie-McHarg answers these questions not by formulating a definition but by tracing a genealogy. He uncovers two crucial strands of contemporary conspiracy theorizing on the threshold of modernity: on the one hand, political analysis as realized by Niccolò Machiavelli in such works as The Prince and, on the other, apocalyptic prophecy as channeled by the charismatic preacher Girolamo Savonarola. The French Revolution, the antisemitic hoax known as the Protocols of the Elders of Zion, and the Nuremberg Trials number among the subsequent episodes that progressively entangled these strands before finally knotting them into the twentieth-century concept of conspiracy theory. Alternative labels were also offered, most strikingly by the historian Richard Hofstadter, whose engagement with American right-wing politics in the 1950s and 1960s inspired his notion of the paranoid style. As McKenzie-McHarg shows, Hofstadter's coinage, with its psychological bent, contributed to personalizing our understanding of conspiracy theory, thus yielding a specific type of person that, for better or worse, has become all too familiar to us today: the conspiracy theorist. Proceeding from The Prince through The Protocols to the paranoid style and then beyond to QAnon, The Hidden History of Conspiracy Theory sheds new light on a complex and troubling phenomenon.