1966–1969: NFL vs. AFL—The beginning of the Super Bowl era[edit]
For a list of AFL Championship Games and winners, see American Football League Championship Game.
For a list of NFL Championship Games and winners, see List of NFL champions (1920–69).
For a list of AFL-NFL World Championship games, see List of Super Bowl champions § AFL-NFL World Championships.
In 1966, the success of the rival AFL, the… More spectre of the NFL's losing more stars to the AFL, and concern over a costly "bidding war" for players precipitated by the NFL's Giants' signing of Pete Gogolak, who was under contract to the AFL's Buffalo Bills, led the two leagues to discuss a merger. Pivotal to this was approval by Congress of a law (PL 89-800) that would waive jeopardy to anti-trust statutes for the merged leagues. The major point of the testimony given by the leagues to obtain the law was that if the merger were permitted, "Professional football operations will be preserved in the 23 cities and 25 stadiums where such operations are presently being conducted." The merger was announced on June 8, 1966, and became fully effective in 1970.

The Packers defeated the Chiefs in the first AFL–NFL Championship Game (Super Bowl I)
After expanding to enfranchise the New Orleans Saints in 1967, the NFL split its 16 teams into two conferences with two divisions each: the Capitol and Century Divisions in the Eastern Conference, and the Coastal and Central Divisions in the Western Conference. The playoff format was expanded from a single championship game to a four-team tournament, with the four divisional champions participating. The two division winners in each conference met in the "Conference Championships", with the winners advancing to the NFL Championship Game. Again, the home team for each playoff game was determined by a yearly divisional or conference rotation.

The AFL on the other hand, raised its total franchise number to ten with the Miami Dolphins joining the Eastern Division in 1966 and the Cincinnati Bengals joining the Western Division in 1968. The league until 1969 kept using the one-game-playoff format except when division tie-breakers were needed. In its final season, 1969, the AFL adopted a four-team playoff to determine its champion.

Following the NFL and AFL Championship Games for the 1966 through 1969 seasons, the NFL champion played the AFL champion in Super Bowls I through IV, the only true inter-league championship games in the history of professional football. The first two of these games were known as the AFL-NFL Championship Game, as the title Super Bowl was not chosen until 1968. Thus the third AFL-NFL matchup was dubbed "Super Bowl III" and the first two matches were retronamed as Super Bowls I and II. The first two games were convincingly won by the NFL's Packers, the last two by the AFL's New York Jets and Kansas City Chiefs, leaving the leagues even at 2-2 in "Championship" competition when they subsequently merged.

All participants in those four AFL-NFL championship games were either AFL champions or NFL champions in the record books, no matter the outcome of the Super Bowl. Three of the four league champions who lost one of the first four Super Bowls would eventually win at least one. The exception is the Minnesota Vikings which went to three others and lost all of them. Less