In order to finance the Civil War, Congress authorizes the U.S. Department of the Treasury to issue non-interest-bearing Demand Notes. These notes earn the nickname “greenbacks” because of their color. All U.S. currency issued since 1861 remains valid and redeemable at full face value.

By 1862, the Demand Notes incorporate fine-line engraving, intricate geometric lathe work patterns, a U.S. Department of the Treasury seal, and engraved signatures to aid in counterfeit deterrence. To this day, U.S. currency continues to add features to deter counterfeiting.

Congress authorizes a new class of currency, known as “United States notes,” or “Legal Tender notes.” These notes are characterized by a red seal and serial number. They continue to circulate until 1971.
 

Congress establishes a national banking system and authorizes the U.S. Department of the Treasury to oversee the issuance of National Banknotes. This system sets Federal guidelines for chartering and regulating "national" banks and authorizes those banks to issue national currency secured by the purchase of United States bonds.

The Bureau of Engraving and Printing begins engraving and printing the faces and seals of U.S. banknotes. Before this, U.S. banknotes were produced by private banknote companies and then sent to the Bureau of Engraving and Printing for sealing, trimming, and cutting.

Legislation mandates that all banknotes and other securities containing portraits include the name of the individual below the portrait. This is why you see names below the portraits on banknotes to this day.

The Federal Reserve Act of 1913 establishes the Federal Reserve as the nation’s central bank and provides for a national banking system that is more responsive to the fluctuating financial needs of the country. The Federal Reserve Board issues new currency called Federal Reserve notes.

The appearance of U.S. banknotes changes greatly in 1929. In an effort to lower manufacturing costs, all Federal Reserve notes are made about 30 percent smaller—measuring 6.14 x 2.61 inches, rather than 7.375 x 3.125 inches. In addition, standardized designs are instituted for each denomination, decreasing the number of designs in circulation and making it easier for the public to distinguish between genuine and counterfeit notes.

Because United States notes no longer served any function not already adequately met by Federal Reserve notes, their issuance was discontinued and, beginning in 1971, no new United States notes were placed into circulation.

A security thread and microprinting are introduced in Federal Reserve notes to deter counterfeiting by copiers and printers. The features first appear in Series 1990 $100 notes. By Series 1993, the features appeared on all denominations except $1 and $2 notes.

In the first significant design change since the 1920s, U.S. currency is redesigned to incorporate a series of new counterfeit deterrents. Issuance of the new banknotes begins with the $100 note in 1996, followed by the $50 note in 1997, the $20 note in 1998, and the $10 and $5 notes in 2000.

The new-design $10 note features subtle background colors of orange, yellow, and red. The $10 note includes an embedded security thread that glows orange when illuminated by UV light. When held to light, a portrait watermark of Treasury Secretary Alexander Hamilton is visible from both sides of the note. In addition, the note includes a color-shifting numeral 10 in the lower right corner of the note.