It is estimated that some 60 million Americans own about 200 million guns. This implies more than one gun per American household. Naturally, such an average conceals enormous variation across households and communities. Gun ownership is uncommon in suburbs like Scarsdale and Winnetka, while most households have guns in the inner cities of major cities, like Chicago, Detroit, or Los Angeles. It is not simply the immense number of guns that makes gun control so difficult, but also the fact that the great majority is illegal and not officially registered.