"The "Big Four" agency groups in the advertising and marketing industry refers to WPP, Omnicom, Publicis Groupe, and Interpublic Group of Companies (IPG). These four holding companies control a large portion of the global advertising and marketing landscape."[https://www.google.com/search?q=big+four+agency+groups&rlz=1C1GCEA_enUS1157US1157&oq=big+four+agency+groups&gs_lcrp=EgZjaHJvbWUyBggAEEUYOdIBCDYxNTFqMGo0qAIAsAIB&sourceid=chrome&ie=UTF-8]