In college football, the Bowl Championship Series, better known as the BCS, was the first college postseason format to automatically create a championship game between the (supposed) 1st and 2nd-best teams in the NCAA's Football Bowl Subdivision.
Prior to the creation of the BCS in 1998, there was no guaranteed method of making sure the #1 and #2 teams played each other after the regular season. Conferences agreed to have their champions meet in specific bowl games, and the "national champion(s)" were decided by a variety of sources.
The BCS was created in 1998 between the four biggest bowl games: the Fiesta, Orange, Rose, and Sugar Bowls. The National Championship Game was to be hosted at one of these four bowls, with the venue rotating every year. The conference champions of the ACC, Big East, Big Ten, Big 12, Pac-10, and SEC were combined with two other "at-large" teams to create the field of eight for these four games.
In 2006, the BCS expanded to include two more at-large teams and a National Championship Game separate from the bowl it was held at (for example, at the end of the 2001 season, the Rose Bowl was the BCS National Championship Game, but at the end of the 2009 season, there was a Rose Bowl and a separate BCS National Championship Game at the Rose Bowl a week later). The host of the title game still rotated, and conference champions still maintained their traditional bowl matchups when possible.
The BCS used a combination of press and coach voting, as well as computer methods, to determine the final rankings. This was reformed over the years regarding which specific polls and computer methods to use, but the consensus was that the BCS may have got it wrong on multiple occasions, including 2001, 2003, 2004, 2008, and 2011.
The BCS also prioritized programs from top conferences, excluding teams like Utah, TCU, and Boise State from the National Championship Game despite going undefeated in their regular seasons. Starting in 2004, the BCS allowed these "mid-major" teams to compete in BCS bowls as at-large teams if they were ranked in the top-12 of the final BCS rankings. These "BCS Busters" went 4-1 in their BCS bowl games, none of which were National Championships.
Dissatisfaction from fans, writers, coaches, and even Barack Obama with the BCS eventually led to its replacement with the College Football Playoff starting after the 2013 regular season. While the Playoff is widely regarded as an improvement from the BCS, it is still criticized for not including teams outside the "Power Five" conferences.