Questions: Which are the main vegetation types of lowland hay meadows and pastures inWestern and Central Europe?What are themain environmental gradients that drive patterns of species composition? Is it possible to classify these grasslands to phytosociological alliances that reflectmanagement practices? Location: Western and Central Europe (excluding the Alps and Carpathians). Methods: A database of 21 400 vegetation plots of mesic grasslands acrossWestern and Central Europe was compiled. After geographically stratified resampling, semi-supervised classification based on the K-means algorithm was applied to assign a subset of plots into 32 a priori association-level vegetation types and to search for new typeswithin the subset of non-assigned plots. The vegetation plots assigned into the final vegetation types were submitted to another K-means classification to showthe grouping into higher-level vegetation types. Results: A total of 36 associations were distinguished in the resampled subset of 8277 vegetation plots and were grouped into four large groups: (1) eutrophic and intensively managed hay meadows and permanent pastures; (2) nutrient-rich grasslands developed from recently abandoned fields or managed under irregular practices of mowing and manuring; (3) non-eutrophic lowland and submontane hay meadows; (4) extensively managed pastures and Atlantic grazed hay meadows. A PCoA of the associations of these four groups showed that extensively managed pastures were floristically more similar to non-eutrophic hay meadows than to permanent intensively managed pastures,which wasmore obvious in the Atlantic region than in Central Europe. Species composition of the lowland hay meadows was clearly differentiated according to biogeographic sectors. Other floristic differenceswere related to climate, altitude, soil base status and topography. Conclusions: This analysis challenges the traditional concept ofmesic grassland alliances separating hay meadows from pastures. New classification should be based mainly on the differences in management intensity rather than in management practice. Consequently, nutrient-poor extensive pastures, which currently are not considered in the European Habitats Directive, should receive the same conservation attention as low-intensive hay meadows, because both types of vegetation can be equally species-rich and do not differ substantially in floristic composition from each other.