This paper is aimed at laying the groundwork for the application of operational research to European air traffic flow management (ATFM). It is based on a project carried out at the EUROCONTROL Central Flow Management Unit (CFMU), the organisation that manages traffic flows in the 36 states belonging to the European Civil Aviation Conference. The paper describes the making of the CFMU, its organisation and systems, the different measures, levels of planning and stakeholders in ATFM and how flow managers carry out their work. In so doing the paper identifies potential applications of operational research to European ATFM, and describes a re-routing demonstrator developed to illustrate different decision support possibilities for re-routing measures. (C) 2000 Elsevier Science B.V. All rights reserved.