Conspiratorial thinking does not mean believing in the existence of conspiracies, which have never ceased to exist in truth. Conspiratorial thinking is the tendency to see conspiracies everywhere and to believe that conspiracies are the key to everything, or almost everything, that happens in the world. The prominent French philosopher and historian of ideas Pierre-André Taguieff analyzes in this book, with both insight and humor, the conspiracy theories that are spread through oral tradition, the Internet, public debate, Hollywood films and populist politics. World history is filled with real conspiracies that achieved their goal or failed miserably. But it is also fraught with speculative or imaginary conspiracies attributed to particular minorities or power (governments, secret services, etc.), conspiracies believed to be true and certain. In a world filled with uncertainties and fears, the proliferation of conspiracy theories and their rapid spread to very large sectors of the population are a remarkable phenomenon for research, and it is quite beneficial for every democratic citizen to understand their function. Conspiracy theories, absurd as they are, have the advantage of "interpreting" facts and providing a simple and coherent image of the world in which nothing seems random anymore, but all, even the scariest, are explainable.