The Omnicom Group (NYSE: OMC) is one of the worl's largest advertising agency holding company in terms of revenue (and one of the big six advertising holding companies; the other companies are WPP Group plc, Interpublic, Publicis, Dentsu and Havas). Its major holdings include the advertising agency networks BBDO, TBWA Worldwide, and DDB Worldwide. Its portfolio of companies also includes public relations, lobbying, marketing services, interactive design, and media buying services.