The posting system is a baseball player transfer system that operates between Nippon Professional Baseball (NPB) and Major League Baseball (MLB). Despite the drafting of the United States – Japanese Player Contract Agreement, unveiled in 1967 to regulate NPB players moving to MLB, problems began to arise in the late 1990s. Some NPB teams lost star players without compensation, an issue highlighted when NPB stars Hideo Nomo and Alfonso Soriano left to play in MLB after using loopholes to void their existing contracts. A further problem was that NPB players had very little negotiating power if their teams decided to deal them to MLB, as when pitcher Hideki Irabu was traded to an MLB team for which he had no desire to play. In 1998, the Agreement was rewritten to address both problems; the result was dubbed the "posting system".

Hideki Irabu was a Japanese professional baseball player of American and Japanese mixed ancestry. He played professionally in both Japan and the United States. Irabu played for the Lotte Orions / Chiba Lotte Marines and Hanshin Tigers of Nippon Professional Baseball (NPB) and for the New York Yankees, Montreal Expos, and Texas Rangers of Major League Baseball (MLB).