The National Banking Acts of 1863 and 1864 were two United States federal banking acts that established a system of national banks chartered at the federal level, and created the United States National Banking System. They encouraged development of a national fiat currency backed by bank holdings of U.S. Treasury securities and established the Office of the Comptroller of the Currency as part of the United States Department of the Treasury. The Act shaped today's national banking system and its support of a uniform U.S. banking policy.

At the end of the Second Bank of the United States in 1836, the control of banking regimes devolved mostly to the states. Different states adopted policies including a total ban on banking (as in Wisconsin), a single state-chartered bank (as in Indiana and Illinois), limited chartering of banks (as in Ohio), and free entry (as in New York). While the relative success of New York's "free banking" laws led several states also to adopt a free-entry banking regime, the system remained poorly integrated across state lines. Though all banknotes were uniformly denominated in dollars, notes would often circulate at a steep discount in states beyond their issue.

In the end, well-publicized frauds arose in states like Michigan, which had adopted free entry regimes but did not require the redeemability of bank issues for specie. The perception of dangerous "wildcat banking”, along with the poor integration of the U.S. banking system, led to increasing public support for a uniform national banking regime.

The United States government, on the other hand, still had limited taxation capabilities and so had an interest in the seigniorage potential of a national bank. In 1846, the Polk Administration created a United States Treasury system that moved public funds from private banks to Treasury branches to fund the Mexican–American War. However, the revenue generated this way was limited without a national currency.

This became more urgent during the Civil War, when Congress and Lincoln were struggling to finance the war efforts. Without a national mechanism for issuing currency other than metal coinage, the Lincoln administration could not exploit the powers and loopholes that, for example, Britain could with its central bank, in order to finance the high expenses involved. Previously, the damage that would be done to state banks by national competition was sufficient to prevent significant national bank chartering. But using the war crisis, Lincoln was able to expand this effort.

One of the first attempts to issue a national currency came in the early days of the Civil War when Congress approved the Legal Tender Act of 1862, allowing the issue of $150 million in national notes known as greenbacks and mandating that paper money be issued and accepted in lieu of gold and silver coins. The bills were fiat money backed only by the national government's promise to redeem them and their value was dependent on public confidence in the government as well as the ability of the government to give out specie in exchange for the bills in the future. Many thought this promise backing the bills was about as good as the green ink printed on one side, hence the name "greenbacks."

The Second Legal Tender Act, enacted July 11, 1862, a Joint Resolution of Congress, and the Third Legal Tender Act, enacted March 3, 1863, expanded the limit to $450 million. The largest amount of greenbacks outstanding at any one time was calculated as $447,300,203.10.

The National Bank Act (ch. 58, 12 Stat. 665; February 25, 1863), originally known as the National Currency Act, was passed in the Senate by a 23–21 vote, and was supplemented a year later by the National Banking Act of 1864. The goals of these acts was to create a single national currency, a nationalized bank chartering system, and to raise money for the Union war effort. The Act established national banks that could issue National Bank Notes which were backed by the United States Treasury and printed by the government itself. The quantity of notes that a bank was allowed to issue was proportional to the bank's level of capital deposited with the Comptroller of the Currency at the Treasury. To further control the currency, the Act taxed notes issued by state and local banks, essentially pushing non-federally issued paper currency out of circulation.