The Climax Series (クライマックスシリーズ, Kuraimakkusu Shirīzu) 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.
Both leagues play a regular season, after which the top three teams in each league compete against one another in a two-stage playoff. In the first stage, the teams that finish the regular season with the second- and third-best records play one another in a best-of-three series. The winners of these three-game series advance to the final stage to face each league's regular-season champion in a six-game series, which the regular-season champion starts with a one-game advantage. The winners of each league's final stage series compete against one another in that year's Japan Series.