This Special Section collects eight articles from the 16th IWA Intational Conference on Diffuse Pollution and Eutrophication (16th DIPCON),which was held in Beijing on 18 to 23 August,2013.These articles focus on the diffuse pollution problems encountered in the development process.rnDiffuse pollution is usually discharged into water systems by routes other than pipes and mostly occurs during rainfall events.Since the 1980s,this problem has been well documented in industrial countries and has been incorporated into regional pollution control programs.However,in most of the developing countries,the people and govment agencies do not know diffuse pollution well.Although people have noticed a decline of water quality after heavy precipitation events and even fish kills in some cases,most people are unaware of the threat of diffuse pollution.In many countries,diffuse pollution is not considered in their environmental monitoring programs.Since rainfall flow discharges are usually not monitored,the diffuse pollution load,which is related to hydrological conditions,is often very much underestimated.