The Agricultural and Related Industries Study Group of the Operational Research Society held a one-day meeting on ‘Modelling Approaches to the Control of Agricultural Pollution’ on 12 November 1991 at Silsoe Research Institute. The group promotes the use of the scientific method in solving management problems. The aim of the meeting was to look at different ways in which modelling could contribute to the understanding and hence control of different types of pollution. Contrasts were the order of the day, with the first talk being a complex mass of differential equations and the second talk describing an expert system with a few simple design equations. Model dimensions ranged from point sources for silage effluent to several farms for invertebrate populations. A common theme was the difficulty of validating models faced with the extremely variable and difficult-to-obtain experimental data.