McCann Erickson is an advertising agency on Madison Avenue in New York City. They are one of Sterling Cooper Draper Pryce's primary competitors.
Because of the impending sale of Puttnam, Powell, and Lowe, which owned Sterling Cooper Advertising Agency, to McCann, Lane Pryce was convinced to free Don Draper, Bertram Cooper, and Roger Sterling from their employment contracts to start Sterling Cooper Draper Pryce. ("Shut the Door. Have a Seat")
After several years of trying to snatch Don and competing for accounts, Jim Hobart finally got what he wanted in 1969 when Roger Sterling agreed to sell him half the agency and 5 year contracts from the partners of Sterling Cooper & Partners with the exception of Jim Cutler. The sale was meant as a play by Roger to save Don's job and get rid of Jim Cutler, however after several months it was discovered by the partners, that as a subsidiary of McCann it cost too much to remain independent and would be dissolved into their parent company.