The present publication is an overview of the latest research related to diffuse pollution originating from runoff from various land use, agricultural surfaces, urban and rural areas and forest resources. The subject matter of diffuse pollution has been presented in the publication with the principles of assessment of diffuse water pollution, quantification of diffuse pollution, methods of mathematical modelling of diffuse pollution, main input data required for diffuse pollution modelling on the pilot area of the Kolubara Catchment in the Republic of Serbia. And finally, the recommendations derived from the project findings and related to water management plan, institutional capacity building in the field of environmental and agricultural statistics. The present publication is intended for various interested users: ranging from those who have heard for the first time about diffuse pollution, down to experts in water protection who may find it useful in solving different problems.