The 2005 NCAA Division I-A football season was the highest level of college football competition in the United States organized by the National Collegiate Athletic Association (NCAA). The regular season began on September 1, 2005 and ended on December 3, 2005. The postseason concluded on January 4, 2006 with the Rose Bowl, which served as the season's BCS National Championship Game.
 
The USC Trojans and the Texas Longhorns finished the regular season as the only undefeated teams in Division I-A and consequently met in the Rose Bowl to play for the national title. Texas defeated USC largely due to the performance of quarterback Vince Young, who gained 467 yards of total offense and ran for three touchdowns. The Longhorns won their first national championship since 1970, and their first consensus national title since 1969. A major conference realignment occurred prior to the 2005 season, when 18 teams in Division I-A changed conferences.
 Temple was expelled from the Big East Conference while Army ended its brief affiliation with Conference USA, resulting in both schools becoming Independents.
 Boston College left the Big East to become the 12th member of the Atlantic Coast Conference (ACC), allowing the league to split into two divisions and hold an annual championship game.
 Cincinnati, Louisville and South Florida left Conference USA to join the Big East. Texas Christian University also left Conference USA to become the Mountain West Conference's ninth member.
 Despite its losses, Conference USA added six schools to increase its membership to twelve, poaching Marshall and UCF from the Mid-American Conference and Rice, Southern Methodist, Tulsa, and UTEP from the Western Athletic Conference (WAC). Like the ACC, Conference USA split into two divisions and started a conference championship game.
 The Western Athletic Conference added Idaho, New Mexico State and Utah State from the Sun Belt Conference.
 The Sun Belt picked up I-AA Independents Florida Atlantic and Florida International.
 Steve Spurrier returned to college coaching for the first time since 2001 after a stint in the NFL, leading South Carolina to a respectable 7–5 season. Urban Meyer, after leading Utah to an undefeated season in 2004, took over at Florida (Spurrier's old school). Charlie Weis left the New England Patriots to become head coach at alma mater Notre Dame, taking the team to a BCS bowl.
 Longtime head coaches Barry Alvarez of Wisconsin and Bill Snyder of Kansas State, both of whom took struggling programs to national prominence during their tenures, retired. Dan Hawkins, having helped make Boise State a powerhouse in the Western Athletic Conference, left the Broncos to coach struggling Colorado.
 Rankings reflect the AP Poll. Rankings for Week 8 and beyond will list BCS Rankings first and AP Poll second. Teams that failed to be a top 10 team for one poll or the other will be noted.
 Heisman Trophy voting was primarily for three players: Reggie Bush, Matt Leinart (who won the trophy in 2004) and Vince Young. Bush won the trophy, with Young (who helped Texas win their first national championship since 1970) second in the voting:
 In June 2010 the NCAA ruled that Bush had received "improper benefits", violating NCAA policy. On September 14, he announced in a statement from the New Orleans Saints that he would forfeit his 2005 Heisman Trophy. Runner-up Vince Young said that he would not accept the trophy if Bush forfeited it. On September 15, the Heisman Trust announced that the 2005 trophy would be vacated and there would be no winner for the season.
 Texas scored the most points (652).