Nippon Professional Baseball or NPB is the highest level of baseball in Japan. Locally, it is often called Puro Yakyū, meaning Professional Baseball. Outside of Japan, it is often just referred to as "Japanese baseball". The roots of the league can be traced back to the formation of the Greater Japan Tokyo Baseball Club in 1934 and the original Japanese Baseball League. NPB was formed when that league reorganized in 1950.

Nippon Professional Baseball consists of two leagues, the Central League and the Pacific League. There are also two secondary-level professional minor leagues, the Eastern League and the Western League, that play shorter schedules.
The season starts in late March or early April and ends in October with two or three all star games in July. In recent decades, the two leagues each scheduled 130, 135 or 140 regular season games with the best teams from each league going on to play in the "Nippon Series" or Japan Series. Starting in 2004, the Pacific League has had a postseason tournament to determine who advances to the Japan Series while the Central League initially did not. That changed in 2007, when the Central League adopted the Pacific League's tournament as well and the tournament became known as the Climax Series with the two winners, one from each league, competing in the Japan Series.