Howard Morton Metzenbaum (born June 4, 1917) is an American politician who served for almost 20 years as a Democrat in the U.S. Senate (1976 - 1995).

Metzenbaum, a Jew, was born in Cleveland, Ohio and received a bachelor's degree from Ohio State University (Columbus, Ohio) in 1939 and a law degree from the same university in 1941. He practiced law in Cleveland before being elected an Ohio state representative, in which office he served from 1943 to 1947. He then served as an Ohio state senator from 1947 to 1951. In 1958, he was the campaign manager for U.S. Sen. Stephen M. Young (D-Ohio).

In 1970, Metzenbaum ran for the U.S. Senate to replace his former employer, Young, defeating John Glenn in the Democratic primary. But Metzenbaum lost to Robert Taft Jr. in the general election. Metzenbaum then ran a group of weekly newspapers in the Cleveland area.

In 1974, when U.S. Sen. William B. Saxbe (R-Ohio) resigned from his seat to accept the nomination as U.S. attorney general, Ohio Gov. John J. Gilligan appointed Metzenbaum to fill out the remainder of Saxbe's term. Metzenbaum ran for election to the seat, but in a bitter Democratic primary, Metzenbaum lost to former astronaut Glenn, a former Marine and the first American ever to orbit the earth. Glenn won the seat in the general election.

In 1976, however, Metzenbaum ran again for the Senate and defeated the incumbent Republican, Robert Taft Jr.. Taft resigned the seat a few days before his term ended, allowing Metzenbaum to be sworn in a few days early and hence have a small edge in seniority over other Senators newly elected in 1976. In 1982, Metzenbaum was re-elected to the seat, defeating frequent Republican candidate Paul E. Pfeifer. In 1988, Metzenbaum was opposed by re-election by George V. Voinovich, who accused Metzenbaum of being soft on child pornography. Voinovich's charges were roundly criticized by many, including by U.S. Sen. John H. Glenn, Metzenbaum's old-time rival in the Democratic Party and now Senate colleague who now came to Metzenbaum's aid, recording a statement for television refuting Voinovich's charges. Metzenbaum won the election in a landslide.

In 1994, Metzenbaum decided not to run for the seat again. His son-in-law, Joel Hyatt, was nominated by the Democrats to replace him, but Hyatt lost to Michael DeWine, the lieutenant governor under Voinovich, who after having been trounced by Metzenbaum in the 1988 Senate race, was elected governor of Ohio in 1990.

While in the Senate, Metzenbaum was a powerful liberal. Although he did not hold an official party leadership position, the Senate Democrats knew that almost nothing would get through if Metzenbaum opposed it. Metzenbaum took a particular interest in antitrust and consumer protection issues, often threatening to repeal the exemption from antitrust laws given to Major League Baseball. Since his retirement, however, the issue has gone largely unaddressed. Metzenbaum became well-known for his service on the Senate Judiciary Committee, particularly because of his dedicated efforts to keep stringent antitrust laws and his pro-choice stance on abortion.

Since 1995, Metzenbaum has served as the chairman of the Consumer Federation of America.

Metzenbaum's cousin, James Metzenbaum, was a prominent Ohio attorney who wrote a noted text on zoning law and once ran for a seat on the Ohio Supreme Court.