What is the relationship between criminality and biology? Nineteenth-century phrenologists insisted that criminality was innate, inherent in the offender’s brain matter. While they were eventually repudiated as pseudo-scientists, today the pendulum has swung back. Both criminologists and biologists have begun to speak of a tantalizing but disturbing possibility: that criminality may be inherited as a set of genetic deficits that place one at risk to commit theft, violence, or acts of sexual deviance. But what do these new theories really assert? Are they as dangerous as their forerunners, which the Nazis and other eugenicists used to sterilize, incarcerate, and even execute thousands of supposed “born” criminals? How can we prepare for a future in which leaders may propose crime-control programs based on biology?