The Siege of Yorktown, also known as the Battle of Yorktown and the surrender at Yorktown, was the final major land engagement of the American Revolutionary War. It was won decisively by the Continental Army, led by George Washington, with support from the Marquis de Lafayette and French Army troops, led by the Comte de Rochambeau, and a French Navy force commanded by the Comte de Grasse, defeating the British Army commanded by British Lieutenant General Charles Cornwallis.

The French and American armies united north of New York City during the summer of 1781. Following the arrival of dispatches from France that included the possibility of support from the French West Indies fleet of the Comte de Grasse, disagreements arose between Washington and Rochambeau on whether to ask de Grasse for assistance in besieging New York or in military operations against a British army in Virginia. On the advice of Rochambeau, de Grasse informed them of his intent to sail to the Chesapeake Bay, where Cornwallis had taken command of the British army. Cornwallis, at first given confusing orders by his superior officer, Henry Clinton, was eventually ordered to build a defensible deep-water port, which he began to do at Yorktown. Cornwallis's movements in Virginia were shadowed by a Continental Army force led by Gilbert du Motier, Marquis de Lafayette.

When word of de Grasse's decision to engage the British navy at the Chesapeake Bay arrived in New York, the American and British armies began moving south toward Virginia, engaging in deception tactics to lead the British to believe a siege of New York was planned. De Grasse sailed from the West Indies and arrived at Chesapeake Bay at the end of August, bringing additional troops and creating a naval blockade of Yorktown. In the beginning of September, he defeated a British fleet led by Sir Thomas Graves, which was dispatched to relieve Cornwallis at the Battle of the Chesapeake. As a result of this victory, de Grasse blocked any reinforcement or escape by sea for Cornwallis and also disembarked the heavy siege guns required by the allied land forces. Washington and Rochambeau arrived at Yorktown on September 28, 1781. Washington moved the army closer to the British defenses on September 29. The American and French army and naval forces had completely surrounded Cornwallis.

After initial preparations, the Americans and French built their first parallel and began the bombardment. With the British defense weakened, on October 14, 1781, Washington sent two columns to attack the last major remaining British outer defenses. A French column under Vicomte de Deux-Ponts took Redoubt No. 9 and an American column under Lieutenant Colonel Alexander Hamilton took Redoubt No. 10. With these defenses, the allies were able to finish their second parallel. With the Franco-American artillery closer and its bombardment more intense than ever, the British position began to deteriorate rapidly. Cornwallis asked for capitulation terms on October 17. After two days of negotiation, the surrender ceremony occurred on October 19; Cornwallis was absent from the ceremony. With the capture of more than 7,000 British soldiers, negotiations between the United States and Great Britain began, resulting in the Treaty of Paris of 1783.

On December 20, 1780, Benedict Arnold sailed from New York with 1,500 British troops to Portsmouth, Virginia. He first raided Richmond, defeating the defending militia, from January 5–7 before falling back to Portsmouth. Admiral Destouches, who arrived in Newport, Rhode Island, in July 1780 with a fleet transporting 5,500 soldiers, was encouraged by Washington and French Lieutenant General Rochambeau to move his fleet south, and launch a joint land-naval attack on Arnold's troops. The Marquis de Lafayette was sent south with 1,200 men to help with the assault. However, Destouches was reluctant to dispatch many ships, and in February sent only three. After they proved ineffective, he took a larger force of eight ships in March 1781, and fought a tactically inconclusive battle with the British fleet of Marriot Arbuthnot at the mouth of the Chesapeake Bay. Destouches withdrew due to the damage sustained to his fleet, leaving Arbuthnot and the British fleet in control of the bay's mouth.

On March 26, Arnold was joined by 2,300 troops under command of Major General William Phillips, who took command of the combined forces. Phillips resumed raiding, defeating the militia at Blandford, then burning the tobacco warehouses at Petersburg on April 25. Richmond was about to suffer the same fate, but Lafayette arrived. The British, not wanting to engage in a major battle, withdrew to Petersburg on May 10.

On May 20, Charles Cornwallis arrived at Petersburg with 1,500 men after suffering heavy casualties at the Battle of Guilford Courthouse. He immediately assumed command, as Phillips had recently died of a fever. Cornwallis had not received permission to abandon the Carolinas from his superior, Henry Clinton, but he believed that Virginia would be easier to capture, feeling that it would approve of an invading British army.

With the arrival of Cornwallis and more reinforcements from New York, the British Army numbered 7,200 men. Cornwallis wanted to push Lafayette, whose force now numbered 3,000 men with the arrival of Virginia militia. On May 24, he set out after Lafayette, who withdrew from Richmond, and linked forces with those under the command of Baron von Steuben and Anthony Wayne. Cornwallis did not pursue Lafayette. Instead, he sent raiders into central Virginia, where they attacked depots and supply convoys, before being recalled on June 20. Cornwallis then headed for Williamsburg, and Lafayette's force of now 4,500 followed him. General Clinton, in a confusing series of orders, ordered Cornwallis first to Portsmouth and then Yorktown, where he was instructed to build fortifications for a deep water port.