A keiretsu (系列?, lit. system, series, grouping of enterprises, order of succession) is a set of companies with interlocking business relationships and shareholdings. It is a type of informal business group. The keiretsu maintained dominance over the Japanese economy for the last half of the 20th century.[1]

The member 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 innovative projects. It is a key element of the automotive industry in Japan.