Federal Yellow book  (Washington, Monitor, Inc.);  Latest edition located at Law Library Reference Desk JK6 .F45

United States Government Manual (National Archives and Record Service. Office of the Federal Register)
1935-present can now be found online.
Lockwood Ref Desk JK 421 .A3 (current edition)
Lockwood Documents US AE 2.108/ 2

This official handbook of the federal government is a directory to all three branches of government. Entries describe the functions and authorities of agencies. Data include the names, addresses, and phone numbers of top administrators. Special features include lists of international organizations in which the U.S. participates; commonly used abbreviations and acronyms; and names of agencies that were eliminated or reorganized.

How to Contact Your Elected Officials 
USA.gov is an information portal that attempts to be a one-stop shopping place for retrieving federal government information. This section provides links to contact information for  elected government officials at all levels.

United States Congress

Congress.org (Capitol Advantage)
Enter your zip code to determine the names and addresses of your Congresspersons and Senators. Links lead to selected key votes and positions on popular issues.

Congressional Directory (U.S. Congress), biennial.
Lockwood Ref Desk  Reference JK 1011 (current edition)
Lockwood Documents US Y 4.P 93/ 1: 1/ (previous editions)
A directory to the federal government that emphasizes Congress. Data about the legislative branch covers phone numbers, addresses, and biographies of Senators and Representatives; committee memberships and committee staff; and maps of Congressional districts. Additional information about other branches of government includes addresses and phone numbers of legislative and executive agencies, and selected federal courts. The Congressional Directory also provides names, addresses, and phone numbers of international agencies in which the U.S. participates; and addresses and phone numbers of foreign embassies in Washington.

Congressional Staff Directory (Congressional Staff Directory, Ltd.), published three times a year.
Lockwood Reference JK 1012 .C66 (current edition)
Lockwood Book Collection JK1012 .C66 (previous editions)
A directory to Congress and its staff. Emphasis is upon Washington staffs of Representatives and Senators and their committees. Information includes phone numbers, and postal and email addresses. When searching for information about a policy issue, staff of relevant Congressional committees could be very helpful. Committee staff often distribute Congressional hearings, reports, and committee prints without charge upon request.

House of Representatives
Links lead to home pages of Representatives and to the House leadership.

United States Senate
Lists members of the Senate and those in leadership positions.

United States Representatives Abroad

Websites of U.S. Embassies Consulates, and Diplomatic Missions  (Department of State)
Links to United States embassies and consulates in other countries, arranged by region.

 U.S. States Policy and Supporting Positions (Plum Book)  Lists more than 9,000 Federal civil service leadership and support positions in the executive and legislative branches that may be subject to noncompetitive appointment.

United States Government Manual (National Archives and Record Service. Office of the Federal Register).
This official handbook of the federal government is a directory to all three branches of government. Entries describe the functions and authorities of agencies. Data includes the names, addresses, and phone numbers of top administrators. Special features include lists of international organizations in which the U.S. participates; commonly used abbreviations and acronyms; and names of agencies that were eliminated or reorganized.

Congressional Directory U.S. Congress)

A  directory to the federal government that emphasizes Congress. Data about the legislative branch covers phone numbers, addresses, and biographies of Senators and Representatives; committee memberships and committee staff; and maps of Congressional districts. Additional information about other branches of government include addresses and phone numbers of legislative and executive agencies, and selected federal courts. The Congressional Directory also provides names, addresses, and phone numbers of international agencies in which the U.S. participates; and addresses and phone numbers of foreign embassies in Washington.