The numerical and functional significance of the Wadden Sea over the past 30 years for twelve wader species is analysed. These species are: Ringed Plover Charadrius hiaticula, Grey Plover Pluvialis squatarola, Red Knot Calidris canutus, Sanderling Calidris alba, Curlew Sandpiper Calidris ferruginea, Dunlin Calidris alpina, Bar-tailed Godwit Limosa lapponica, Eurasian Curlew Numenius arquata, Spotted Redshank Tringa erythropus, Redshank Tringa totanus, Greenshank Tringa nebularia, and Ruddy Turnstone Arenaria interpres. The results of wader counts and wader catching activities are described per species. For every species attention is paid to the spatial distribution within the area, the seasonal changes, and the changes over the past 30 years with respect to the numbers of waders. The population composition is analysed with respect to the geographical breeding origin as deduced from morphometrics, sex ratio and/or age composition, and the changes in primary moult and body mass in the course of the non-breeding season. Findings with respect to the breeding origins were obtained by comparing the wing- and culmen lengths of waders captured in the Wadden Sea with the measurements of skins collected in a series of zoological museums at the northern hemisphere.