The Culper Ring was a network of spies active during the American Revolutionary War, organized by Major Benjamin Tallmadge and General George Washington in 1778 during the British occupation of New York City. The name "Culper" was suggested by George Washington and taken from Culpeper County, Virginia. The leaders of the spy ring were Abraham Woodhull and Robert Townsend, using the aliases of "Samuel Culper Sr." and "Samuel Culper Jr.", respectively; Tallmadge was referred to as "John Bolton".

While Tallmadge was the spies' direct contact, Washington often directed their operations. The ring was tasked to provide Washington information on British Army operations in New York City, the British headquarters. Its members operated mostly in New York City, Long Island, and Connecticut between late October 1778 and the British evacuation of New York in 1783.

The information supplied by the spy ring included details of a surprise attack on the newly arrived French forces under Lieutenant General Rochambeau at Newport, Rhode Island, before they had recovered from their arduous sea voyage, as well as a British plan to counterfeit American currency on the actual paper used for Continental dollars, which prompted the Continental Congress to retire the bills.

The ring also informed Washington that Tryon's raid of July 1779 was intended to divide his forces and allow Lieutenant General Sir Henry Clinton to attack them piecemeal. In 1780, the Culper Ring discovered that a high-ranking American officer, subsequently identified as Benedict Arnold, was plotting with British Major John André to turn over the vitally important American fort at West Point, New York on the Hudson River and surrender its garrison to the British forces.^{[citation needed]}

Before British Major General William Howe's move from Staten Island, George Washington had received information of varying utility from individual spies working independently and without significant direction, such as Lawrence Mascoll. After evacuating the Continental Army from Brooklyn Heights, Washington asked William Heath and George Clinton to set up "a channel of information" on Long Island, but he did not yet try to establish permanent agents behind enemy lines.

Instead, he sought volunteers for espionage missions. Among them was Captain Nathan Hale, who went to New York City under a false identity but was quickly captured by the British and executed on September 22, 1776. This made Washington realize that a more discreet and well-organized espionage system would be necessary to infiltrate British operations. He decided that civilians would attract less attention than soldiers, and he asked William Duer to recommend a suitable agent. Duer recommended Nathaniel Sackett; his army contact was Hale's former classmate, then Captain Benjamin Tallmadge.

Sackett had some success, for example, the discovery that the British were building flat-bottomed boats for a campaign against Philadelphia; however, Washington felt he did not produce enough correct intelligence fast enough, and Sackett was soon paid off. Early in 1777, American Colonel Elias Dayton set up a spy network on Staten Island, which worked with an established network known as the Mersereau Ring.

The British victory at the Battle of Brandywine on September 11, 1777, led to the capture of Philadelphia on September 26, which became a new focus of intelligence gathering. Washington assigned this task to Major John Clark. Recently returned to service after being wounded before Brandywine, Clark set up a successful network, but poor health forced him to take up a desk job.