The National League Championship Series (NLCS), also known as the National 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. It is contested by the winners of the two National League (NL) Division Series. The winner of the NLCS wins the NL pennant and advances to the World Series, MLB's championship series, to play the winner of the American League's (AL) Championship Series. The NLCS began in 1969 as a best-of-five playoff and used this format until 1985, when it changed to a best-of-seven format.

The National League of Professional Baseball Clubs, known simply as the National League (NL), is the older of two leagues constituting Major League Baseball (MLB) in the United States and Canada, and the world's oldest extant professional team sports league. Founded on February 2, 1876, to replace the National Association of Professional Base Ball Players (NAPBBP) of 1871–1875, the NL is sometimes called the Senior Circuit, in contrast to MLB's other league, the American League, which was founded 25 years later and is called the "Junior Circuit". Both leagues currently have 15 teams.