The first large-scale paper currency issued by the United States federal government was the United States Note.
United States Notes, originally called legal-tender notes, were created during the Civil War. The Legal Tender Act of 1862 authorized the federal government to issue paper money that could be used to pay debts, except certain public obligations such as customs duties and interest on federal bonds.
Their nickname, “greenbacks,” came from the green ink used on their reverse sides. Unlike banknotes issued by private commercial banks, United States Notes were obligations of the federal government. They helped finance the Union war effort when tax revenue and borrowing alone were insufficient.
Federal Reserve Notes later became the dominant US paper currency after the Federal Reserve System began issuing them in 1914. United States Notes remained legal tender but were discontinued from issuance in 1971. They are therefore distinct from both Continental currency and modern Federal Reserve Notes.