Max Sieben Baucus (born December 11, 1941) is the senior United States Senator (United States Senate) from Montana and a member of the Democratic Party (Democratic Party (United States)). First elected to the Senate in 1978, and as of 2010 he is the longest-serving Senator from Montana, and the sixth longest-serving U.S. Senator currently in office.

As the current chairman of the Senate Committee on Finance (United States Senate Committee on Finance), Baucus has played an influential role in the debate over health care reform in the United States. He is also chairman of the Joint Committee on Taxation (United States Congress Joint Committee on Taxation), and a member of the Senate Committee on Agriculture, Nutrition and Forestry (United States Senate Committee on Agriculture, Nutrition and Forestry) and Senate Committee on Environment and Public Works (United States Senate Committee on Environment and Public Works), where is chairman of the Subcommittee on Transportation and Infrastructure (United States Senate Environment and Public Works Subcommittee on Transportation and Infrastructure).

Before his election to the Senate, Baucus was a member of the United States House of Representatives from 1975 to 1978, representing Montanas (now defunct) 1st congressional district (Montanas 1st congressional district). He previously served in the Montana House of Representatives from 1973 to 1974.