INTRODUCTION FP is a CFD (computational fluid dynamics) method coded in Fortran for calculating the flow field and aerodynamic forces of an isolated wing (denoted usually as a wing-alone) or a wing-body combination (denoted usually as a wing-body) in a subsonic freestream@ including the effects of shock waves. FP uses a relaxation process to solve finite-difference forms of the full nonlinear velocity-potential equation for the flow around the three-dimensional geometry. The FP program was developed over a period of years at ARA@ Bedford and RAE (now QinetiQ)@ Farnborough@ and is made available by ESDU International plc under the terms of an agreement with QinetiQ. Used originally on mainframe computers@ FP has provided valuable data in the design of a number of aircraft. With advances in computers@ it has become possible to perform runs of FP on a PC within a few minutes. The FP code results presented in this Item have all been produced from runs on a PC. The version described takes no account of the boundary layer or viscous wake@ but it is intended that an enhanced version (denoted VFP) that does take account of viscous effects@ albeit in a simplified manner@ will be issued subsequently. The guide for running FP comprises Part 2@ and is issued as a separate Data Item (Reference 1). This Item provides an account of the principles of FP@ a number of results@ and comparisons with other methods and with experiment. In common with other CFD codes@ FP comprises two distinct elements@ the grid generator and the flow solver. The main features of these elements are described in Section 3. The performance of FP is considered in Sections 4 and 5. In Section 4@ some basic results for subcritical flows are presented first@ followed by results for flows with shock waves. Comparisons with experimental data are given in Section 5@ and these indicate typical differences between inviscid and real flows. In Section 6 remarks are made concerning the accuracy and applicability of FP.