This CFD Guide provides Best Practice Guidelines recommended by ESDU for the modelling, using Computational Fluid Dynamics (CFD), of pressure and flow characteristics in circular pipes with sudden contractions in incompressible flow. These Guidelines are based on extensive CFD validation studies by ESDU, described in ESDU TN 06023 and used in ESDU 05024, and may be used with any RANS CFD code with low-Reynolds-number turbulence modelling capabilities for the modelling of sharp-, round- and chamfer-edged sudden contractions in laminar and turbulent incompressible flow.