This chapter discusses the principles of flight planning, the information required and the messages exchanged between the various agents. Procedures and relevant information have been drawn together from a number of sources, with a particular focus on EUROCONTROL handbooks and manuals associated with the current Central Flow Management Unit System (the suite of software known as ‘CFMU 11’). An example passenger flight is used to help explain how a flight plan1 is prepared and the processes involved in getting an aircraft airborne. Although this chapter focuses on flights operating in Europe under instrument flight rules (IFR), occasional comparisons are made with non-European flight planning and visual flight rules (VFR).