In Belgium, as in most countries, each Minister or Secretary is assisted by a limited number of trusted collaborators who constitute the Ministerial Office («Cabinet», «Kabinet»). The article is an attempt to shed a light on the Chief Ministerial Officer («Chef de Cabinet», «Kabinetschef») who is the closest collaborator of the Minister. In order to show the role of the Chief Ministerial Officer, the article first describes the tasks, powers and composition of the Ministerial Office to proceed to a more extensive analysis of the functions, the appointment of the Chief Ministerial Officer, and the question whether he can exercise executive power. The most important tasks of the Chief Ministerial Officer are: organization and coordination of the Office and its activities, acting as a «Liaison-Officer» with the Minister, passing on of information, exercising of a form of internal, political and administrative control. The article closes with some more personal remarks, pointing out a few guidelines which a Chief Ministerial Office, should keep in mind.