An advertising agency, often referred to as a creative agency or an ad agency, is a business dedicated to creating, planning, and handling advertising and sometimes other forms of promotion and marketing for its clients. An advertising agency, often referred to as a creative agency or an ad agency, is a business dedicated to creating, planning, and handling advertising and sometimes other forms of promotion and marketing for its clients. An advertising agency, often referred to as a creative agency or an ad agency, is a business dedicated to creating, planning, and handling advertising and sometimes other forms of promotion and marketing for its clients.