The USA has a problem with incarceration. Since 1970, the number of people incarcerated has climbed from less than 500 000 to 2·3 million. Despite only 5% of the world's population living in the country, the USA imprisons nearly 25% of all incarcerated people globally; the highest rate of imprisonment in the world. The sheer scale of imprisonment in the USA and its unequal burden on people from minority and poor backgrounds raises concerns about its impact on the health and wellbeing of the national population. While black Americans account for only 13% of the country's population, they make up 40% of its prison population, according to the Vera Institute of Justice. A black man born from 2001 onward has a one in three chance of being incarcerated in his lifetime; this compares with one in 17 for their white counterparts. For black women the chance is one in 18, compared with one in 111 for white women. People from poor communities are also far more likely to go to prison.