President Pro Tempore of the United States Senate
Incumbent Chuck Grassley since January 3, 2025
Style	Mr./Mrs. President (Informal and within the Senate) The Honorable (Formal)
Appointer	Elected by the U.S. Senate
Inaugural holder	John Langdon April 6, 1789
Formation	U.S. Constitution March 4, 1789
Succession	Third

The president pro tempore (/ˌproʊ ˈtɛmpəriː/ or /ˌproʊ ˈtɛmpəreɪ/),^[1] or president pro tem, of the United States Senate is the longest serving senator from the majority political party in the United States Senate. According to the Constitution, this is the fourth highest office in the United States. It is the third in the U.S. presidential line of succession (behind the vice president and the speaker of the House). Many state senates also use the office of President pro tem.

Officially the vice president is the person in charge of the Senate, but they are not a Senator. Chuck Grassley (R-IA) is the current president pro tempore since January 3, 2025^[update]. When the vice president cannot be in charge, the president pro tempore is in charge of the Senate. Many people still think of the president pro tempore as de facto president of the Senate. Benjamin Wade was only one vote away from becoming the president of the United States due to the impeachment of Andrew Johnson. No president pro tempore has ever taken over the presidency.

Probably the most famous presidents pro tempore were John Langdon (first in this office), David Rice Atchison (D-MO), Benjamin Wade (R-OH), Arthur Vandenberg (R-MI), Carl Hayden (D-AZ) Richard Russell, Jr. (D-GA), Strom Thurmond (R-SC), Robert Byrd (D-WV), Daniel Inouye (D-HI), Orrin Hatch (R-UT), Chuck Grassley (R-IA) and Patrick Leahy (D-VT).

When Senator Hubert Humphrey, a former vice president, was seriously ill, the Senate showed its respect for him by creating the office of Deputy President Pro tempore for any former president or vice president who is elected to the Senate. No vice president since Humphrey has held this.

Since 2001, the honorary title of president pro tempore emeritus has been given to a Senator of the minority party who has previously served as president pro tempore. The position has been held by:

• Strom Thurmond (R-South Carolina) (2001-2003)
• Robert Byrd (D-West Virginia) (2003-2007)
• Ted Stevens (R-Alaska) (2007-2009)^[2]
• Patrick Leahy (D-Vermont) (2015-2021)
• Chuck Grassley (R-Iowa) (2021-2025)
• Patty Murray (D-Washington) (since 2025)