There are five main categories of congressional staff: personal staff, committee staff, leadership staff, institutional staff, and support agency staff. Within each category, there are a wide variety of positions, ranging from Chief of Staff to janitors and the Capitol Police. A large number of staff employed are partisan and are linked to a particular party or member of Congress, but there are also a large number of non-partisan staff whose role it is to keep Congress operational.
According to the Cable-Satellite Public Affairs Network (C-SPAN), there were approximately 24,000 congressional staff members in 2011. Overall staffing levels have changed over the centuries. Numbers were relatively low in the 19th century, but expanded during the 1930s and expanded to their more recent levels in the 1970s.
Personal staff are the congressional staff hired by each member of Congress to run their congressional office. These staff are divided into two basic types: Washington D.C. staff and district staff. District staff include the District Director and those who cover the constituency of the member of Congress.
Historically, there were few personal staff within Congress. In 1893, each member of Congress was permitted to hire only two official staff. This grew to 18 members of staff and four temporary staff by 1979. Staffing levels and office structure vary from congressperson to congressperson.
Many congressional offices are overseen by the Chief of Staff. Below the Chief of Staff there are legislative, communication, and casework teams. Members of Congress also tend to hire personal secretaries, congressional aides, and a legislative counsel.
Committee staff were first permitted in the 1830s, although there were no permanent clerks until 1856. Each member of a committee, whether of the majority or minority party, hire clerks, press secretaries, researchers and investigators, and a counsel to help with the workload a committee involves. These workers tend to be hired because of their specific knowledge relating to the committee's interests. There are, however, four committees where members are not allowed to hire their own staff: the House Committee on Standards of Official Conduct, the House Permanent Select Committee on Intelligence, the Senate Select Committee on Ethics, and the Senate Select Committee on Intelligence.
The institutional staff are the congressional staff who keep Congress running. They are divided into partisan and non-partisan staff. The partisan staff are hired by the majority and minority leaders of both the House and the Senate in order to help them organize both houses and to keep legislation moving. Both the majority and minority whips also hire institutional staff to help them whip members into voting the right way.
There are many types of non-partisan institutional staff members. First, there are the capitol police, who keep order and deal with all criminal matters. There is also an office called "Architect of the Capitol," which includes all of the cleaning and maintenance staff who deal with the physical structure of the institution itself.
Support agency staff are non-partisan and work for the different congressional agencies, including the Congressional Research Service, the Government Accountability Office, and the Congressional Budget Office. Although the head of each agency is appointed by, or in collaboration with, members of Congress, each agency is expected to be non-partisan and objective. Staff members of these agencies provide research and information to members of Congress from all political parties.