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The Congressional office buildings are the office buildings used by the United States Congress to augment the limited space in the United States Capitol. The Congressional office buildings are part of the Capitol Complex, and are thus under the authority of the Architect of the Capitol and protected by the United States Capitol Police. The office buildings house the individual offices of each U.S. Representative and Senator as well as committee hearing rooms, staff rooms, multiple cafeterias, and areas for support, committee, and maintenance staff.
The Congressional office buildings are connected to the Capitol by means of underground pedestrian tunnels, some of which are equipped with small railcars shuttling users to and from the Capitol, which together form the Capitol subway system. Congressional pages are responsible for carrying packages and messages from the two chambers to the buildings.
The three Senate office buildings are along Constitution Avenue north of the Capitol:
The three House office buildings are along Independence Avenue south of the Capitol:
A fifth building, the O'Neill House Office Building (previously known as "House Annex-1") was named after former Speaker of the House Thomas "Tip" O'Neill. The building was demolished in 2002. However, in 2008, Federal Office Building No. 8 (formerly the headquarters of the Food and Drug Administration was renovated, being renamed the O'Neill House Office Building in 2012. The building was transferred from General Services Administration to the Architect of the Capitol in 2017. It currently houses both House administrative staff as well as offices for the Department of Health and Human Services.
The U.S. Capitol Complex also includes a Page Residence Hall and a Capitol Power Plant, both on the House side of the Capitol.