Nippon Professional Baseball (日本野球機構, Nippon Yakyū Kikō; NPB) is a professional baseball league and the highest level of baseball in Japan. Locally, it is often called Puro Yakyū (プロ野球), meaning simply Professional Baseball; outside of Japan, NPB is often referred to as "Japanese baseball".
The roots of the league can be traced back to the formation of the "Greater Japan Tokyo Baseball Club" (大日本東京野球倶楽部, Dai-Nippon Tōkyō Yakyū Kurabu) in 1934. The first professional circuit for the sport in Japan, the Japanese Baseball League (JBL), was founded two years later and continued to play even through the final years of World War II. The organization that is today's NPB was formed when the JBL reorganized in 1950, dividing its 15 teams into two leagues, which would meet in the annual season-ending Japan Series championship playoff series of games starting that year.