Capitol Hill is a neighborhood in Washington, D.C., located in both the Northeast and Southeast quadrants. It is bounded by 15th Street SE & NE, F Street NE, Southeast Boulevard SE, and South Capitol Street SE. Dominated by the United States Capitol, which sits on the highest point of Capitol Hill, it is one of the oldest historic districts in Washington. The neighborhood has a high concentration of rowhouses, largely dating from the 19th century. Home to around 35,000 people in just under 2 square miles (5 km²), Capitol Hill is also one of the most densely populated neighborhoods in Washington. The name Capitol Hill is frequently used as a metonym for the U.S. Congress.

Capitol Hill is famed as a center of the United States government, home to numerous important institutions including the U.S. Congress, the Supreme Court, the Library of Congress, and more. Apart from government, the neighborhood is largely residential, but maintains notable commercial hubs along Pennsylvania Avenue, such as Eastern Market and Barracks Row.

Pierre Charles L'Enfant selected the location of the United States Capitol (the "Congress House") in his 1791 design for the federal capital city (see: L'Enfant Plan). The building would be the symbolic center of his plan. He referred to the hill chosen as the site of the future Congress House as "Jenkins Hill" or "Jenkins Heights".

However, the tract of land had for many years belonged to the Carroll family and was noted in their records of ownership as "Rome". While a man named Thomas Jenkins had once pastured some livestock at the site of the Capitol (and thus his name was associated with the site), artist John Trumbull, who would paint several murals inside the Capitol's rotunda, reported in 1791 that the site was covered with a thick wood, making it an unlikely place for livestock to graze. Research published in 2004 by the Capitol Hill Historical Society showed that Jenkins' land was seven blocks east of the site of the Capitol and that L'Enfant was likely to have given Jenkins' name to the general location.

While serving in 1793 as President George Washington's secretary of state, Thomas Jefferson named Capitol Hill, invoking the famous Temple of Jupiter Optimus Maximus on the Capitoline Hill, one of the seven hills of Rome. However, the connection between the two is not completely clear.

The neighborhood that is now called Capitol Hill started to develop when the government began work at two locations, the Capitol and the Washington Navy Yard. It became a distinct community between 1799 and 1810 as the federal government became a major employer. The first stage in its early history was that of a boarding house community developed for members of Congress. In the early years of the Republic, few Congressmen wished to establish permanent residence in the city. Instead, most preferred to live in boarding houses within walking distance of the Capitol.

In 1799, the Washington Navy Yard was established on the banks of the Anacostia River, providing jobs to craftsmen who built and repaired ships. Many of the craftsmen who were employed both at the Navy Yard and in the construction of the Capitol chose to live within walking distance, to the east of the Capitol and the north of the Navy Yard. They became the original residential population of the neighborhood.

In 1801, Thomas Jefferson, who was at the time President of the United States, selected the location of the Marine Barracks, which had to be within marching distance of both the Capitol and the White House, near the Washington Navy Yard. By 1810, shops, goldsmiths, blacksmiths, and churches were flourishing in the area.