Barbara Ann Mikulski (born July 20, 1936) is an American politician and social worker who served as a United States senator from Maryland from 1987 to 2017. A member of the Democratic Party, she also served in the United States House of Representatives from 1977 to 1987. Mikulski is the third-longest-serving female United States Senator, and the longest-serving U.S. Senator in Maryland history.

Raised in the Fell's Point neighborhood of East Baltimore, Mikulski attended Mount Saint Agnes College and the University of Maryland School of Social Work. Originally a social worker and community organizer, she was elected to the Baltimore City Council in 1971 after delivering a highly publicized address on the "ethnic movement" in America. She was elected to the House of Representatives in 1976, and in 1986, she became the first woman elected to the United States Senate from Maryland.

From the death of Senator Daniel Inouye in December 2012 until 2015, Mikulski chaired the Senate Appropriations Committee. She was the first woman and first Marylander to hold the position. At her retirement, she was the ranking minority member of the committee. She also served on the Health, Education, Labor, and Pensions Committee and the Select Committee on Intelligence.

On March 2, 2015, Mikulski announced that she would retire after five terms in the Senate and would not seek reelection in 2016. In January 2017, Mikulski joined Johns Hopkins University as a professor of public policy and advisor to University President Ronald J. Daniels.