Advertising agencies are independent organizations that provide specialized advertising and promotion services to help companies develop, prepare, and execute their advertising programs. They offer services like marketing analysis, creative development, media planning/placement, and research. Agencies have skilled specialists in areas like creative, media, research, and account management. They are organized into departments led by directors and coordinated by account executives responsible for client relationships. Agencies earn commissions from media buys or charge fees, and aim to gain new clients through referrals, presentations, and reputation while retaining existing clients through good performance and communication.