The Braddock Expedition, also known as Braddock's Campaign or Braddock's Defeat, was a British military expedition which attempted to capture Fort Duquesne from the French in 1755 during the French and Indian War. The expedition, named after its commander General Edward Braddock, was defeated at the Battle of the Monongahela on July 9 and forced to retreat; Braddock was killed in action along with more than 500 of his troops. It ultimately proved to be a major setback for the British in the early stages of the war, one of the most disastrous defeats suffered by British forces in the 18th century.

Braddock's expedition was part of a massive British offensive against the French in North America that summer. As commander-in-chief of the British Army in America, General Edward Braddock led the main thrust against the Ohio Country with a column some 2,100 strong. His command consisted of two regular line regiments, the 44th and 48th, in all 1,400 regular soldiers and 700 provincial troops from several of the Thirteen Colonies, and artillery and other support troops. With these men, Braddock expected to seize Fort Duquesne easily, and then push on to capture a series of French forts, eventually reaching Fort Niagara. George Washington, promoted to Lieutenant-Colonel of the Virginia Regiment on June 4, 1754, by Governor Robert Dinwiddie, was then just 23, knew the territory and served as a volunteer aide-de-camp to General Braddock. Braddock's Chief of Scouts was Lieutenant John Fraser of the Virginia Regiment. Fraser owned land at Turtle Creek, had been at Fort Necessity, and had served as Second-in-Command at Fort Prince George (replaced by Fort Duquesne by the French), at the confluence of the Allegheny and Monongahela Rivers.

Braddock mostly failed in his attempts to recruit Native American allies from those tribes not yet allied with the French; he had but eight Mingo Indians with him led by George Croghan, serving as scouts. A number of Native Americans in the area, notably Delaware leader Shingas, remained neutral. Caught between two powerful European empires at war, the local Native Americans could not afford to be on the side of the loser. They would decide based on Braddock's success or failure.

According to returns given June 8, 1755, at the encampment at Will's Creek.

Detachement under Capt. Robert Hind

Setting out from Fort Cumberland in Maryland on May 29, 1755, the expedition faced an enormous logistical challenge: moving a large body of men with equipment, provisions, and (most importantly, for attacking the forts) heavy cannons, across the densely wooded Allegheny Mountains and into western Pennsylvania, a journey of about 110 miles (180 km). Braddock had received important assistance from Benjamin Franklin, who helped procure wagons and supplies for the expedition. Among the wagoners were two young men who would later become legends of American history: Daniel Boone and Daniel Morgan. Other members of the expedition included Ensign William Crawford and Charles Scott. Among the officers of the expedition were Thomas Gage, Charles Lee, future American president George Washington, and Horatio Gates.

The expedition progressed slowly because Braddock considered making a road to Fort Duquesne a priority in order to effectively supply the position he expected to capture and hold at the Forks of the Ohio, and because of a shortage of healthy draft animals. In some cases, the column was only able to progress at a rate of two miles (about 3 km) a day, creating Braddock's Road — an important legacy of the march — as they went. To speed up movement, Braddock split his men into a "flying column" of about 1,300 men which he commanded, and, lagging far behind, a supply column of 800 men with most of the baggage, commanded by Colonel Thomas Dunbar. They passed the ruins of Fort Necessity along the way, where the French and Canadians had defeated Washington the previous summer. Small French and Native American war bands skirmished with Braddock's men during the march.

Meanwhile, at Fort Duquesne, the French garrison consisted of only about 250 French marines and Canadian militia, with about 640 Native American allies camped outside the fort. The Native Americans were from a variety of tribes long associated with the French, including Ottawas, Ojibwas, and Potawatomis. Claude-Pierre Pécaudy de Contrecœur, the Canadian commander, received reports from Native American scouting parties that the British were on their way to besiege the fort. He realised he could not withstand Braddock's cannon, and decided to launch a preemptive strike, an ambush of Braddock's army as he crossed the Monongahela River. The Native American allies were initially reluctant to attack such a large British force, but the French field commander Daniel Liénard de Beaujeu, who dressed himself in full war regalia complete with war paint, convinced them to follow his lead.