The 2006 United States Senate elections were held on November 7, 2006, with all 33 Class 1 Senate seats being contested. The term of office for those elected in 2006 ran from January 3, 2007, to January 3, 2013. Before the election cycle, the Republican Party controlled 55 of the 100 Senate seats.
The Senate elections were part of the Democratic sweep during the 2006 elections, in which Democrats made numerous gains and no congressional or gubernatorial seat held by a Democrat was won by a Republican. However, Democratic incumbent Joe Lieberman in Connecticut was defeated in the primary and was later reelected as a third-party candidate; he continued to caucus with the Democrats. Because of this, this is the first time since 1970 in which a member of a third party, who is not an independent, was elected to the Senate. Independent Jim Jeffords in Vermont retired but was succeeded by another Independent, Bernie Sanders, retaining their presence in the Senate. Jeffords and Sanders both caucused with Democrats. Democrats picked 6 seats up by defeating Republican incumbents in Missouri, Montana, Pennsylvania, Ohio, Rhode Island, and Virginia, while holding open seats in Maryland and Minnesota. Republicans held their sole open seat in Tennessee.
Following the elections, no party held a majority of seats for the first time since January 1955. The Democrats were able to control the chamber because the two Independents caucused with the Democrats. They needed at least 51 seats to control the Senate because Vice President Dick Cheney would have broken any 50–50 tie in favor of the Republicans. This was the only time between 1990 and 2022 that Democrats gained Senate seats in a midterm.
As of 2024[ [update]], this was the last time a Democrat won a Senate election in Nebraska, the last time a Democrat did not win a seat in Connecticut, and the last time that the tipping point state was decided by under 1%, with Jim Webb of Virginia winning by a margin of under .4%.
Results summary.
 ;onlyinclude ;Summary of the November 7, 2006, United States Senate election results
"Sources:"
Race summary.
Special elections during the 109th Congress.
There were no special elections during the 109th Congress.
Elections leading to the next Congress.
In these general elections, the winners were elected for the term beginning January 3, 2007; ordered by state.
All of the elections involved the Class 1 seats.
Closest races.
In eight races the margin of victory was under 10%.
Gains and losses.
Retirements.
Two Democrats, one Republican, and one Independent retired rather than seek re-election. 
Defeats.
Six Republicans and one Democrat sought re-election but lost in the primary or general election.
Post-election changes.
One Republican died on June 4, 2007, and was replaced by a Republican appointee on June 22, 2007. One other Republican resigned on December 18, 2007, and was replaced by a Republican appointee on December 31, 2007.
Arizona.
Incumbent Republican Jon Kyl won re-election to a third term over Democrat Jim Pederson, real estate developer and former chairman of the Arizona Democratic Party.
! scope="col" colspan="2" style="width: 15em" |Party
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The incumbent, Republican Jon Kyl, was elected to the Senate in 1994 and was re-elected to a second term in 2000; having previously spent eight years in the U.S. House of Representatives. Kyl's Democratic opponent for the general election was wealthy real-estate developer Jim Pederson, who served as the Arizona Democratic Party Chairman from 2001 to 2005. During his tenure, Pederson spent millions of dollars of his own money to help Democrats modernize and to elect Janet Napolitano as Governor of Arizona. The deadline for signing petition signatures to appear on the September 12, 2006, primary ballot was June 14, 2006.
Not long after the 2004 election, Pederson's name began being mentioned as a potential Senate candidate for the 2006 race. On July 28, 2005, Pederson formally stepped down as Chairman of the Arizona Democratic Party, further fueling those speculations. In early September 2005, an e-mail was sent from the Arizona Democratic Party's website, inviting people to an announcement by Pederson on September 7. In an anticlimactic move, an e-mail was sent out shortly after the first saying that the announcement would be postponed due to Hurricane Katrina. It was requested that any money that would be donated to Pederson's campaign at the announcement be directed to relief efforts instead. Similarly, a meeting in Arizona of the Democratic National Committee (DNC) was scheduled for around the same time. It was also postponed and the same request was made involving donations. On September 7, 2005, Pederson filed to run for the U.S. Senate. On September 14, 2005, Pederson formally announced his intention to run, in his hometown of Casa Grande, Arizona.
Although Kyl started the campaign with a sizable lead in most polls, the gap quickly narrowed, especially after Pederson released his array of ads.
Pederson lost the election by 9.84% or 150,257 votes, despite Democratic Incumbent Governor Janet Napolitano easily being re-elected and winning every county statewide. While Pederson lost it was still notable, as it was the worst performance of Senator Kyl's career. Kyl did well as Republicans usually do in Maricopa County home of Phoenix. Pederson did well in Pima County home of Tucson which tends to support Democrats. Kyl was called the winner by CNN at around 8 P.M. local time, 11 P.M. EST. Pederson called Senator Kyl and conceded defeat at 9:02 p.m. local time, 12:02 A.M. EST.
! scope="col" colspan="2" style="width: 130px"|Party
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! colspan="3" style="text-align: right; margin-right: 0.5em" | Majority
! colspan="3" style="text-align: right; margin-right: 0.5em" scope=row | Turnout
! style="text-align:right;" | Swing
California.
Incumbent Democrat Dianne Feinstein won re-election to her third full term.
The Republican candidate was Dick Mountjoy, who had never held a statewide elected position, but had been a state senator for several years. Also running was Libertarian Michael Metti, Don Grundmann of the American Independent Party, Todd Chretien of the Green Party and Marsha Feinland of the Peace and Freedom Party.
Because California is a state that requires a large amount of money to wage a competitive statewide campaign, it is not unusual - as was the case for this race - for a popular incumbent to have no significant opponent. Several prominent Republicans, such as Bill Jones, Matt Fong, and others, declined to run, and a previous announced challenger, businessman Bill Mundell, withdrew his declaration after determining he would not be a self-funded candidate (like Michael Huffington was in the 1994 election).
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On September 22, the "Los Angeles Times" reported that Mountjoy's official biography, as found on his campaign website, falsely asserted that he had served aboard the battleship "USS Missouri" during the Korean War—he'd actually served aboard the heavy cruiser "USS Bremerton". A review of the ships' logs corroborated this and the website was quickly changed to reflect his service aboard the "Bremerton" rather than the "Missouri". Mountjoy denied having been responsible for adding the incorrect information
Feinstein won the election easily. Feinstein won almost every major urban area, winning in Los Angeles, San Francisco, Sacramento, and San Diego. Feinstein was projected the winner as the polls closed at 11 p.m. EST.
! scope="col" colspan="2" style="width: 15em" |Party
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! colspan="3" style="text-align:right;" | Invalid or blank votes
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! colspan="3" style="text-align: right; margin-right: 0.5em" | Turnout
Connecticut.
Incumbent Democrat Joe Lieberman lost the August 8 Democratic primary to cable executive Ned Lamont, a former Greenwich selectman. Lieberman formed his own third party and won in the general election to a fourth term.
Because Connecticut was believed to be a Democratic stronghold, Connecticut's Senate seat was considered safe to remain as a Democratic seat by political analysts, but Lieberman's continued support for conservative and Bush administration policies made him vulnerable to a Democratic primary challenger. Lieberman's critics objected to what they call Lieberman's lack of commitment to the Democratic party; his opposition to affirmative action; his opposition to a Connecticut state law that would require Catholic hospitals to provide emergency contraception to rape victims; his membership in the bipartisan Gang of 14; his support of Florida governor Jeb Bush in the Terri Schiavo case; his initial willingness to compromise on Social Security privatization; his alliances with Republicans; and his attacks on other Democrats.
On March 13, 2006, Ned Lamont announced his candidacy for the Democratic nomination. Lamont was more liberal than Lieberman, but he was not immune from criticism from within his own party. "The New Republic" senior editor and "liberal hawk" Jonathan Chait criticized Lamont's supporters by comparing them to activists who he felt "tore the party apart" in the 1960s and 70s.
Early polling showed Lieberman with as much as a 46-point lead, but subsequent polls showed Lamont gaining until Lamont took the lead just weeks before the primary. A controversy about a "kiss" Lieberman supposedly received from President Bush during the 2005 State of the Union address highlighted concerns that the senator was too close to the unpopular president to be a credible Democratic nominee. Lieberman released several campaign advertisements over the summer of 2006, seeking to connect himself to former President Bill Clinton and to portray Lamont as standing for little more than opposition to Lieberman. Lamont struck back against some of Lieberman's more negative ads with an advertisement produced by well-known political consultant Bill Hillsman. In Lamont's ad, a foreboding narrator says, "Meet Ned Lamont. He can't make a decent cup of coffee, he's a bad karaoke singer, and he has a messy desk." Lamont then chimes in, "Aren't you sick of political attack ads that insult your intelligence? Senator Lieberman, let's stick to issues and pledge to support whoever wins the Democratic primary."
From midmorning August 7 to well past August 9, Lieberman's official campaign site was taken offline; officials from Lieberman's campaign claimed, "dirty politics" and "Rovian tactics" on the part of Lamont's supporters, and more specifically, a sustained Distributed Denial of Service attack that, according to the Lieberman campaign, had left the site down for several days.
Tim Tagaris, Lamont's Internet communications director, denied the charge and attributed the downtime to the fact that the Lieberman campaign had chosen an inferior web host, or ISP, and was only paying $15/month to operate its site (in comparison to the $1500/month being spent by the Lamont campaign). On December 20, 2006, a joint investigation by Connecticut Attorney General Richard Blumenthal's office and the U.S. attorney's office cleared the Lamont campaign of the hacking accusations. A spokesman for Kevin O'Connor, the U.S. Attorney for Connecticut, stated, "The investigation has revealed no evidence the problems the Web site experienced were the result of criminal conduct."
Lamont won the primary with 51.79% of the vote, as opposed to Lieberman's 48.21%. However, in his concession speech, Lieberman announced that he would stand by his prior statements that he'd run as an independent if he lost the Democratic primary.
In the Republican Party primary, Alan Schlesinger drew fire in July when it was revealed that he had been gambling under an alias in order to avoid detection as a card counter. Despite calls to withdraw from the race, Schlesinger remained in the race, ultimately becoming the Republican nominee when no other Republican challengers entered the race.
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On June 12, Ned Lamont began running radio ads promising if he lost the primary to endorse Lieberman, challenging Lieberman to abandon consideration of an independent run by making a similar pledge. Lieberman refused to make this pledge; his campaign manager, Sean Smith said, "Are we going to support Ned Lamont? Ah, no!"
On July 3 in Hartford, Lieberman announced that he would collect signatures in order to guarantee himself a position on