An advertising agency is an independent business that creates and handles advertising campaigns for clients. It provides services like research, planning, creative work, media selection, and more. Key departments include account services, creative teams, media planners, production, and researchers. Account services manage client relationships while creative teams develop concepts and ads. Media planners choose appropriate media placements and negotiate deals. Production oversees ad creation. Researchers assess markets and test ideas. Agencies can be full-service and provide all advertising functions, creative boutiques focusing on design, specialized in specific areas, or in-house serving one company.