The United States has less than 5 percent of the world's population. But it has almost a quarter of the world's prisoners. Indeed, the United States leads the world in producing prisoners, a reflection of a relatively recent and now entirely distinctive American approach to crime and punishment. Americans are locked up for crimes - from writing bad checks to using drugs - that would rarely produce prison sentences in other countries. And in particular they are kept incarcerated far longer than prisoners in other nations. Criminologists and legal scholars in other industrialized nations say they are mystified and appalled by the number and length of American prison sentences. The United States has, for instance, 2.3 million criminals behind bars, more than any other nation. The United States ... has 751 people in prison or jail for every 100,000 in population. (If you count only adults, one in 100 Americans is locked up.) The median among all nations is about 125, roughly a sixth of the American rate. Far from serving as a model for the world, contemporary America is viewed with horror," James Whitman, a specialist in comparative law at Yale, wrote last year in Social Research. Prison sentences here have become "vastly harsher than in any other country to which the United States would ordinarily be compared," Michael Tonry, a leading authority on crime policy, wrote.