ESDU 97031 is concerned with the prediction of the wind conditions downstream of the fences. It enables predictions to be made of the change in local wind speed and turbulence intensity compared with conditions in the absence of the fence. Predictions of a shelter factor that takes account of the combined effects of those changes are also included. The prediction method for single fences is extended to groups of parallel fences. A computer program (E9731) of the method is provided on disk in the software volume in the form of a Visual Basic Application running within Microsoft Excel. A fully worked example illustrates the use of the program. The basis of the method is described and guidance is included on reduction of adverse effects of wind that is inclined to the fence and on fences enclosing an area. Typical applications of windbreaks in civil engineering and in agriculture are noted.