Eutrophication has been defined in various ways. Some authors stress the increase in nutrient concentration, especially nitrogen and phosphorus compounds, others the effect of the presence of these nutrients,viz. increase in biomass. A historical survey is given of the origin of the eutrophication concept as developed by NAUMANN and THIENEMANN. In the present paper eutrophication has been defined as the process in water by which the factors which stimulate autotrophic production become optimal. Eutrophication in the Netherlands has been recognized only very recently as an alarming pollution problem. Since about 1975 the problem got serious public and political interest. This resulted in 1979 in the so-called Fosfatennota (‘Phosphate Report’) of the Ministry of Health and Environmental Protection. This report recommends a reduction of phosphate loading in Dutch surface waters to values below 0.5–1.0 g. P.m.−2.y−1. Restoration of eutrophic waters will be a laborious process. A serious question is to what biological situation a water basin must be restored. The description of the ‘original’ situation is particularly difficult. Regarding this some methods are discussed.