The 2008 American League Championship Series (ALCS), the second round of the 2008 American League playoffs, was a best-of-seven series matching the two winners of the American League Division Series. The AL East Division champion Tampa Bay Rays, who had defeated the Chicago White Sox in the ALDS, were paired with the wild-card and defending world champion Boston Red Sox, who had defeated the Los Angeles Angels of Anaheim, in the ALDS. Tampa Bay held the home field advantage.

The American League Championship Series (ALCS), also known as the American League Pennant, is a best-of-seven playoff and one of two League Championship Series comprising the penultimate round of Major League Baseball's (MLB) postseason. The winner of the ALCS wins the AL pennant and advances to the World Series, MLB's championship series, to play the winner of the National League's (NL) Championship Series. The ALCS began in 1969 as a best-of-five playoff and used this format until 1985, when it changed to its current best-of-seven format.