Corporate or central PMOs are often arranged in a hierarchical structure with specific functions being delegated to the various offices. At a strategic level they provide advice and guidance to the executive on the coporate portfolio, look outside the organisation to discover and then inculcate best practices into the organisation, and provide support and guidance to the project and programme communities.
At a divisional or functional level, PMO teams act as consultants to the projects and programmes being undertaken by the organisation. They carry out reviews and health checks on projects to help ensure their success and the capture of lessons learned.
At a tactical level, solo PMOs provide support to individual projects or programmes, often in the form of administrative or specialist staff (e.g. planners, risk managers).