Omnicom Group, Inc. is an American global marketing and corporate communications holding company, headquartered in New York City. Omnicom's branded networks and speciality firms provide services in four disciplines: advertising, customer relationship management (CRM), public relations and speciality services. The services included in these disciplines are media planning and buying, digital and interactive marketing, sports and events marketing, field marketing and brand consultancy.

Omnicom Group was ranked as one of the four largest advertising agencies in the world by The New York Times in 2002. In 2014, Omnicom was considered the second largest advertising holding company by The Wall Street Journal.