In the time before Slan begins, there was a world war that destroyed civilization around the world, leaving humanity in mis ery. Out of the destruction arose a new dictatorial government that revived old technologies. In Jommy Cross's time, the thirtysixth century, humanity has colonized the moon and is poised to travel to other worlds.

In spite of technological advances, most of humanity lives in an unpleasant society, stuffed into cramped living quarters. This makes the society of Slan a dystopia, or a society that represents some of the worst aspects of human experience.

The government's biggest challenge has arisen during the events chronicled in Slan.

A new species of human has developed, seemingly everywhere at once. Calledslans, these people have odd tendrils on their heads and are telepathic. Fearing them, people have killed them, and the government's secret police hunt them down in order to exterminate them...