The Corps of Discovery was a specially-established unit of the United States Army which formed the nucleus of the Lewis and Clark Expedition that took place between May 1804 and September 1806. The Corps was led jointly by Captain Meriwether Lewis and Second Lieutenant William Clark. Commissioned by President Thomas Jefferson, the Corps' objectives were scientific and commercial to study the area's plants, animal life, and geography, and to learn how the Louisiana Purchase could be exploited economically. An additional group of scouts, boatmen, and civilians aided the Corps.

The Lewis and Clark Expedition from August 31, 1803, to September 25, 1806, also known as the Corps of Discovery Expedition, was the United States expedition to cross the newly acquired western portion of the country after the Louisiana Purchase. The Corps of Discovery was a select group of U.S. Army and civilian volunteers under the command of Captain Meriwether Lewis and his close friend Second Lieutenant William Clark. The expedition made its way westward, and crossed the Continental Divide of the Americas before reaching the Pacific Coast.

President Thomas Jefferson commissioned the expedition shortly after the Louisiana Purchase in 1803 to explore and to map the newly acquired territory, to find a practical route across the western half of the continent, and to establish an American presence in this territory before European powers attempted to establish claims in the region. The campaign's secondary objectives were scientific and economic: to study the area's plants, animal life, and geography, and to establish trade with local Native American tribes. The expedition returned to St. Louis to report its findings to Jefferson, with maps, sketches, and journals in hand.