Prison overcrowding, also called "prison crowding," is a matter of great contention and concern in current criminal justice public policy debates in both Canada and the United States. Coming to public attention as a social problem most recently in the United States in the late 1970s, prison overcrowding has coincided with the unprecedented growth in the nation's prison population over the past several decades.

Because of the "war on drugs" and mandatory sentencing, the United States has become the world's foremost jailer. With just 5 percent of the world's population, the United States has 25 percent of its prisoners, approximately 2.4 million, a number that steadily increases by about 3 percent each year. In 2006, federal prisons were operating at 37 percent above capacity.

The criminal justice system responded to what some jurisdictions call the "crisis" of prison overcrowding through diversion strategies, relying more heavily on jails for the overflow of prisoners, doubling up prisoners in one cell (also called double bunking), hotly debated early release strategies, and an increasing reliance on private (for-profit) prisons, to name a few. However, policy focus on capacity issues sometimes detracts from the actual conditions of privacy, security, and manageability (including meeting basic needs for nutrition, health, and sanitation) within prisons.

In 2006, the Vera Institute of Justice's Commission on Safety and Abuse in America's Prisons held public hearings, which included expert testimony on prison crowding. The conveners pointed out that no academic literature shows an established connection between overcrowding and violence. However, this research is not from the perspective of corrections officers and inmates whose daily experience may lead them to different conclusions. The debate on overcrowding in part thus hinges on experiential viewpoints and