More than two million people are currently incarcerated in the United States.

While the country accounts for 5 percent of the global population, it is home to 25 percent of the world's prison population.

How can photography help us understand this vast system, and the lives shaped--and disrupted--by mass incarceration?

From a reflection on the origins of the mug shot to stark aerial views of supermax prisons to recent projects focused on everyday life in New York's Riker's Island, Louisiana's Angola Prison, and California's San Quentin Prison, this issue considers the visual record, and human toll, of a national crisis that is often removed from public view.

Prison Nation is organized with contributing editor Nicole Fleetwood, author of the forthcoming book, Carceral Aesthetics: Prison Art and Public Culture.