The League Championship Series (LCS) is the semifinal round of postseason play in Major League Baseball which has been conducted since 1969. In 1981, and since 1995, the two annual series have matched up the winners of the Division Series, and the winners advance to meet in the World Series. The LCS comprises the American League Championship Series (ALCS) and National League Championship Series (NLCS).
The League Championship Series was created in 1969, when both the National League and the American League increased in size from ten teams to twelve with the addition, via expansion, of the Montreal Expos and San Diego Padres to the former and the Kansas City Royals and Seattle Pilots (now the Milwaukee Brewers of the NL) to the latter. Concomitant with this, both leagues formed Eastern and Western Divisions, the first-place teams from which faced off in the LCS.
For its first sixteen seasons, the League Championship Series were best-of-five, using the format in which the team without home field advantage hosted the first two games and the team with it hosted the remaining game(s), making it impossible for the disadvantaged team to win the series at home. It also allowed those teams the unusual luxury of starting a series at home, possibly having home field advantage in a three-game series, and a guarantee that they play the maximum number of games possible at home (2).
In 1985, the LCS was lengthened to best-of-seven games in the format with the team holding home-field advantage opening the series at home and playing the next three games on the road, before returning home for two more possible games. The disadvantaged team would have had more games played at home than on the road if the series ends in five games.
Until 1998, the home-field advantage in the LCS was allocated on a rotating basis between the two (and from 1995 through 1997, among the three) division champions; since 1998 the team with the better record has had this advantage, except that in no case can the wild card ever secure the extra home game, regardless of regular season records.