Chapter 1 discusses how all prisons share essential features. Prisoners, who have either been charged with or convicted of a crime, are forced to relocate to a facility for confinement. Once there, the captive must usually interact with other people in the same situation. They suffer the pains of imprisonment, which often includes deprivation of liberty, goods and services, heterosexual relationships, autonomy, and security. Prisoners tend to come from relatively disadvantaged socio-economic backgrounds. All prisons are based on coercion, and prisoners have no voluntary exit option. The chapter then shows how there is nevertheless, tremendous variation in life behind bars. In some prisons, informal institutions are incredibly important; in others, they are nearly non-existent. In some places, prisoners create hierarchy and organizations to rule; in others, norms prevail. Finally, the chapter outlines how the book will help explain how these different systems of governance arise.