Elections were held in the United States on November 4, 2008, during the war on terror and the onset of the Great Recession. It was considered a Democratic wave election, with Democratic Senator Barack Obama of Illinois defeating Senator John McCain of Arizona by a wide margin, and the Democrats bolstering their majorities in both chambers of Congress, thereby marking the first time since 1992 in which the Democrats won Congress and the presidency in one election, and would not do so again until 2020.

Obama won his party's presidential nomination after defeating Senator Hillary Clinton in the 2008 Democratic primaries. With Republican President George W. Bush term-limited, Senator John McCain of Arizona won the Republican nomination in the 2008 Republican primaries. Obama won the general election with 52.9 percent of the popular vote and 365 of the 538 electoral votes.

Democrats picked up net gains of eight Senate seats and 21 seats in the House of Representatives on the back of Obama's coattail effect. They also won a net gain of one gubernatorial seat. The 2006 elections and 2008 elections represented the first time since 1936 that Democrats or any party made substantial gains in Congress in two consecutive elections.

This was the first presidential election year since 1964 when the Democratic Party won the White House and had coattails in the Senate and House of Representatives. The major theme during the campaign was the American public's general desire for change and reform from both Washington and the policies of President Bush. The economy and other domestic policies were also dominant issues, especially during the last months of the campaign after the onset of the 2008 financial crisis.

Senator Barack Obama of Illinois was the Democratic nominee, and Senator John McCain of Arizona was the Republican nominee. Incumbent President George W. Bush was ineligible for re-election per the Twenty-second Amendment to the United States Constitution, which limits a president to two terms, and incumbent Vice President Dick Cheney declined to run for the office.

The 2008 presidential election was the first since 1952 in which neither an incumbent president nor an incumbent vice president was a candidate.

Senator Obama won the number of electors necessary to be elected president and was inaugurated on January 20, 2009.

The 33 seats in the United States Senate Class 2 were up for election, plus special Senate elections in Mississippi and Wyoming. The resignation of Mississippi Senator Trent Lott, and the death of Wyoming Senator Craig L. Thomas, both Class 1 senators, meant that both of those states' senate seats were up for election. The Democrats gained 8 seats, while the Republicans did not gain a seat.