ESDU 76027 gives a comprehensive survey of all aspects of diffuser performance. It introduces the methods used in ESDU Items (73024 for conical diffusers, 74015 for plane-walled diffusers and 75026 for annular diffusers) to present static pressure recovery and total head loss and illustrates the effect of geometry including cross-section shape. The influence of surface finish, including the effect of the junction with the inlet duct, is illustrated. Various aspects of inlet flow such as velocity profile, swirl, turbulence, Mach number and Reynolds number, are discussed in relation to their effect on performance. Methods of improving performance using splitters, vortex generators, boundary layer control, gauzes, truncation, wall curvature, and other techniques are discussed.