Definition of advertising agency

independent service organization that contracts with advertisers (firms or individuals attempting to find customers for their products and services) to manage their advertising. Historically, advertising agency services are of a creative nature, but the agency concept has expanded to include research services and media planning and buying. Agencies are typically classified by the type of business they handle (e.g., financial, industrial, or consumer packaged goods) or the range of services they offer (e.g., creative, media, or full service).