This list covers 50 of the world's largest advertising agencies, ordered alphabetically, as estimated by agency revenues. The basic premise for inclusion on this list is companies that create advertising material; and they place it - or turn it over for placement to a media buying service - to various dissemination mediums ("media"), such as television, newspapers, magazines, radio, and the Internet. They may also produce traditional direct marketing materials ("Direct Mail" in the sense of historically nationalized Postal Services, i.e., USPS, Royal Mail; Deutsche Post AG; etc). Typically, the largest agencies place their own media; although a few creative-only agencies made this list.
A few major US advertising agencies include units of Interpublic and Omnicom; leading companies based outside the US include Dentsu and Hakuhodo DY Holdings (Japan), Publicis (France), and WPP (Ireland). Omnicom & Publicis Groupe recently announced a "merger of equals" [LINK].
We'll kick off our list with these 5 ad agency companies: