A keiretsu (Japanese: 系列; literally system, series, grouping of enterprises, order of succession) is a set of companies with interlocking business relationships and shareholdings that dominated the Japanese economy in the second half of the 20th century. In the legal sense, it is a type of business group that is in a loosely organized alliance within Japan's business community. It rose up to replace the zaibatsu system that was dissolved in the occupation of Japan following the Second World War. Though their influence has shrunk since the late 20th century, they continue to be important forces in Japan's economy in the early 21st century.
The members' companies own small portions of the shares in each other's companies, centered on a core bank; this system helps insulate each company from stock market fluctuations and takeover attempts, thus enabling long-term planning in projects.