David Skarbek of King's College London and author of The Social Order of the Underworld: How Prison Gangs Govern The American Penal System talks with EconTalk host Russ Roberts about the written and unwritten rules in America's prisons for the most violent and dangerous criminals. Skarbek explains how and why prison gangs emerged in the last half of the 20th century, their influence both inside and outside of prisons, and how their governance structure is maintained.