These days, whenever anything spreads, whether it’s a YouTube fad or a political rumor, we say it went viral. But how does virality actually work? In The Rules of Contagion, epidemiologist Adam Kucharski explores topics including gun violence, online manipulation, and, of course, outbreaks of disease to show how much we get wrong about contagion, and how astonishing the real science is.

Why did the president retweet a Mussolini quote as his own? Why do financial bubbles take off so quickly? Why are disinformation campaigns so effective? And what makes the emergence of new illnesses—such as MERS, SARS, or the coronavirus disease COVID-19—so challenging? By uncovering the crucial factors driving outbreaks, we can see how things really spread—and what we can do about it.

Whether you are an author seeking an audience, a defender of truth, or simply someone interested in human social behavior, The Rules of Contagion is an essential guide to modern life.