Few of us question the slips of green paper that come and go in our purses, pockets, and wallets. Yet confidence in the money supply is a recent phenomenon: prior to the Civil War, the United States did not have a single, national currency. Instead, countless banks issued paper money in a bewildering variety of denominations and designs – more than ten thousand different kinds by 1860. Counterfeiters flourished amid this anarchy, putting vast quantities of bogus bills into circulation. This article, adapted from the 2009 book A Nation of Counterfeiters (Harvard University Press), discusses the origins of American counterfeiting of currency, a story that runs parallel to the story of art forgery.