More than 80 years ago, the federal Home Owners’ Loan Corporation released its “Residential Security” maps, guides of American cities for lenders and brokers infamous for the color they used to condemn black neighborhoods to decades of disinvestment: red. The four-tiered HOLC maps worked to both hamper black home-buying and quash its gains, setting in motion a racial disparity in home values that helps explain today’s racial wealth gap. In some cases, redlining reflected the overcrowded housing conditions characteristic of American ghettos, where black families—denied access to most of the city—were forced to pay exorbitant rates for substandard apartments. But in other cases, the designation simply marked the presence of any black residents at all. Older ethnic neighborhoods with a mix of residences and businesses, such as Manhattan’s Lower East Side and Boston’s South End, were also redlined.