This Data Item introduces the subject of flow in rotating machinery and provides guidance and techniques for modelling specific flow applications involving discs@ cylinders and cavities@ predominantly in steady-state@ stable flow conditions. An interest in the fluid flow associated with rotating machinery may stem from the need to know the mechanical losses and flow structure in electric motors@ centrifugal compressors or rotary pumps. Emphasis within this Data Item has been placed on presenting correlations based on analytical@ experimental and computational fluid dynamics (CFD) models for parameters such as mass flow@ boundary layer thickness@ swirl speed@ pressure distribution and moment@ used in parametric design studies and optimisation. This Data Item includes consideration of laminar@ transitional and turbulent flow for the case of a disc rotating in a fluid. This case is used as the basis for extension to more complex rotating disc applications such as those involving the disc rotating adjacent to a stationary disc with a shroud and superposed supply of fluid@ i.e. rotor-stator wheelspace systems. The cases of a rotating cylinder in a fluid and of an annulus where one or both of the cylinders are rotating are also considered. A common configuration for rotating cavities where two adjacent discs are co-rotating is briefly introduced.