The 89th United States Congress was a meeting of the legislative branch of the United States federal government, composed of the United States Senate and the United States House of Representatives. It met in Washington, D.C., from January 3, 1965, to January 3, 1967, during the second and third years of Lyndon B. Johnson's presidency. The apportionment of seats in the House of Representatives was based on the 1960 United States census.

Both chambers had a Democratic supermajority, and with the election of President Lyndon B. Johnson to his own term in office, maintaining an overall federal government trifecta. This is the last time Democrats or any party had a 2/3rd supermajority in the Senate.

The 89th Congress is regarded as "arguably the most productive in American history".^[1] Some of its landmark legislation includes Social Security Amendments of 1965 (the creation of Medicare and Medicaid), the Voting Rights Act, Higher Education Act, Immigration and Nationality Act of 1965, Elementary and Secondary Education Act and the Freedom of Information Act.

• January 4, 1965: President Johnson proclaimed his "Great Society" during his State of the Union Address.
• January 20, 1965: Inauguration of President Lyndon B. Johnson for a full term.
• November 8, 1966: United States elections, 1966, including:
  • United States Senate elections, 1966
  • United States House of Representatives elections, 1966

• April 11, 1965: Elementary and Secondary Education Act, Pub. L.Tooltip Public Law (United States) 89–10
• July 27, 1965: Federal Cigarette Labeling and Advertising Act, Pub. L.Tooltip Public Law (United States) 89–92
• July 30, 1965: Social Security Act of 1965, Pub. L.Tooltip Public Law (United States) 89–97 (including Medicaid and Medicare)
• August 6, 1965: Voting Rights Act, Pub. L.Tooltip Public Law (United States) 89–110
• August 10, 1965: Housing and Urban Development Act of 1965, Pub. L.Tooltip Public Law (United States) 89–117
• August 26, 1965: Public Works and Economic Development Act of 1965, Pub. L.Tooltip Public Law (United States) 89–136
• September 9, 1965 Department of Housing and Urban Development Act, Pub. L.Tooltip Public Law (United States) 89–174, 79 Stat. 667
• September 29, 1965: National Foundation on the Arts and the Humanities Act, Pub. L.Tooltip Public Law (United States) 89–209
• October 3, 1965: Immigration and Nationality Act of 1965, (Hart-Celler Act, INS Act) Pub. L.Tooltip Public Law (United States) 89–236
• October 6, 1965: Heart Disease, Cancer, and Stroke Amendments, Pub. L.Tooltip Public Law (United States) 89–239
• October 20, 1965: Motor Vehicle Air Pollution Control Act, Pub. L.Tooltip Public Law (United States) 89–272 (including Solid Waste Disposal Act)
• October 22, 1965: Highway Beautification Act, Pub. L.Tooltip Public Law (United States) 89–285
• November 8, 1965: Higher Education Act, Pub. L.Tooltip Public Law (United States) 89–329
• November 8, 1965: Vocational Rehabilitation Act Amendments Pub. L.Tooltip Public Law (United States) 89–333
• August 26, 1966: Laboratory Animal Welfare Act Now called the Animal Welfare Act Pub. L.Tooltip Public Law (United States) 89–544
• April 13, 1966: Uniform Time Act, Pub. L.Tooltip Public Law (United States) 89–387
• July 13, 1966: Cotton Research and Promotion Act, Pub. L.Tooltip Public Law (United States) 89–502
• September 6, 1966: Pub. L.Tooltip Public Law (United States) 89–554, which (among other things) enacted what is now called the Freedom of Information Act
• September 9, 1966: National Traffic and Motor Vehicle Safety Act, Pub. L.Tooltip Public Law (United States) 89–563
• September 9, 1966: Highway Safety Act, Pub. L.Tooltip Public Law (United States) 89–564
• October 15, 1966: National Historic Preservation Act, Pub. L.Tooltip Public Law (United States) 89–665
• October 15, 1966: National Wildlife Refuge System Administration Act of 1966, Pub. L.Tooltip Public Law (United States) 89–669
• October 15, 1966: Department of Transportation Act, Pub. L.Tooltip Public Law (United States) 89–670
• November 2, 1966: Cuban Adjustment Act, Pub. L.Tooltip Public Law (United States) 89–732
• November 3, 1966: Comprehensive Health, Planning and Service Act, Pub. L.Tooltip Public Law (United States) 89–749

• July 6, 1965: Approved an amendment to the United States Constitution addressing succession to the presidency and establishing procedures both for filling a vacancy in the office of the vice president, and for responding to presidential disabilities, and submitted it to the state legislatures for ratification
  • Amendment was later ratified on February 10, 1967, becoming the 25th Amendment to the United States Constitution

The count below identifies party affiliations at the beginning of the first session of this Congress, and includes members from vacancies and newly admitted states, when they were first seated. Changes resulting from subsequent replacements are shown below in the "Changes in membership" section.

• House Democratic Caucus
• Senate Democratic Caucus

This list is arranged by chamber, then by state. Senators are listed in order of seniority, and representatives are listed by district.

Lists of committees and their party leaders for members of the House and Senate committees can be found through the Official Congressional Directory at the bottom of this article. The directory after the pages of terms of service lists committees of the Senate, House (Standing with Subcommittees, Select and Special) and Joint and, after that, House/Senate committee assignments. On the committees section of the House and Senate in the Official Congressional Directory, the committee's members on the first row on the left side shows the chairman of the committee and on the right side shows the ranking member of the committee.