Keiretsu are Japanese business conglomerates with interlocking ownership and business relationships. There are three types: horizontal keiretsu focused on diversified businesses, vertical keiretsu organized around manufacturing networks, and vertical distribution networks. Keiretsu emerged after World War II and differ from pre-war Zaibatsu which had a more centralized ownership structure controlled by founding families. Major modern keiretsu include Mitsubishi, Mitsui, Sumitomo, Fuyo, and Sanwa, with Toyota being the largest vertically integrated keiretsu.