This is a complete list of United States senators during the 106th United States Congress listed by seniority from January 3, 1999, to January 3, 2001.
Order of service is based on the commencement of the senator's first term. Behind this is former service as a senator (only giving the senator seniority within their new incoming class), service as vice president, a House member, a cabinet secretary, or a state governor. The final factor is the population of the senator's state.
Senators who were sworn in during the middle of the two-year congressional term (up until the last senator who was not sworn in early after winning the November 2000 election) are listed at the end of the list with no number.
During the 106th Congress, the U.S. Senate had a Republican majority. In this Congress, Tim Hutchinson was the most junior senior senator, until Paul Coverdell's death on July 18, 2000, after which Max Cleland was the most junior senior senator. Ernest Hollings was the most senior junior senator.
The most senior senators by class were Robert Byrd (D-West Virginia) from Class 1, Strom Thurmond (R-South Carolina) from Class 2, and Daniel Inouye (D-Hawaii) from Class 3.