The Climax Series is the current annual playoff system implemented by Japan's Nippon Professional Baseball (NPB). It determines which team from the Central League (CL) and from the Pacific League (PL) will advance to compete for the championship in the Japan Series. After the creation of the NPB's two-league system in 1950, the PL experimented with three different playoff systems. In 2004, it implemented the postseason structure from which the Climax Series is based. After three seasons, the CL adopted the same system in 2007, creating the current, unified playoff format.

The Nippon Professional Baseball (NPB) playoffs have taken several different forms throughout the organization's history. Japanese baseball is divided into two leagues; the Pacific League (PL) is less popular and less profitable than the Central League (CL). As a result, the PL has employed various playoff formats throughout its history in an effort to increase fan interest. The PL's first true playoff system was introduced in the 1973 season. It involved a split season plan that divided the season into two halves and the two teams that won each half went on to play each other in a five-game playoff series, with the winner advancing to the Japan Series. While popular with fans, the format was scrapped after ten seasons because of major issues and criticisms. In the year following their last split season, the PL returned to a single season, however if five or fewer games separated the first- and second-place teams at the end of the season, the two teams would play each other in a five-game playoff series. This playoff system was unpopular and ridiculed by media and fans. It only lasted three seasons with a playoff series never needing to be played.