The Culper Code Book was the cipher system used by the Culper Spy Ring, the intelligence network organized in 1778 by Major Benjamin Tallmadge (1754–1835) under orders from George Washington (1732–1799) to gather information on British forces in and around occupied New York City. The codebook assigned numbers to 763 words, names, and places, so that sensitive correspondence could be disguised: Washington was 711, New York City was 727, and individual agents operated under aliases and numbers. The surviving codebook, preserved at Mount Vernon, pairs ordinary vocabulary with numerical substitutes, allowing spies to encrypt the names of people and locations alongside everyday language. The codebook is a tangible artifact of revolutionary espionage and a useful entry point for discussing the often-hidden side of the war. It demonstrates that the American victory depended not only on battlefield engagements but also on the careful, dangerous work of gathering intelligence, protecting sources, and outwitting a powerful enemy.