Real conspiracies do exist. Volkswagen conspired to cheat emissions tests for their diesel engines. The U.S. National Security Agency secretly spied on civilian internet users. The tobacco industry deceived the public about the harmful health effects of smoking. We know about these conspiracies through internal industry documents, government investigations, or whistleblowers.

Conspiracy theories, by contrast, tend to persist for a long time even when there is no decisive evidence for them. Those conspiracy theories are based on a variety of thinking patterns that are known to be unreliable tools for tracking reality. Typically, conspiracy theories are not supported by evidence that withstands scrutiny but this doesn’t stop them from blossoming. For example, the widespread belief that the 9/11 terrorist attacks were an “inside job” has persisted for many years after the event.1 Decades after the fact, a vast majority of Americans believe that the government covered up the truth about the JFK assassination.

Conspiracy theories damage society in a number of ways. For example, exposure to conspiracy theories decreases people’s intentions to engage in politics or to reduce their carbon footprint. In order to minimise these harmful effects, The Conspiracy Theory Handbook helps you understand why conspiracy theories are so popular, explains how to identify the traits of conspiratorial thinking, and lists effective debunking strategies.