This document provides a list of major advertising agencies located in Los Angeles, New York, and Chicago. It includes well-known agency names like Ogilvy & Mather, Grey, Saatchi & Saatchi, and JWT. Websites like variety411.com and LinkedIn are recommended to find contact information on agencies. Industry publications like Adage.com and Adweek.com should be read to stay informed on news, trends, awards and brands in the advertising world.