What is the difference between a professional conference organizer (PCO), a travel agency, a conference center, a hotel or a Public Relations officer?

A travel agency, a conference center, a hotel or a PR officer cannot cover the whole range of works needed to a complete conference or event organizing. A PCO, however, specializes in every aspect of the organization and coordination, with full responsibility for budgetary control and liaising, where necessary, with all other suppliers, including those listed above.