Over the past 50 years, major changes have taken place in the distribution of aquatic plants in Europe. Many species have declined in the face of habitat destruction, unsympathetic management of existing habitats, or the acidification or eutrophication of freshwaters. Other species have increased in abundance or spread, including several that were originally introduced from the New World. Focusing on the relative richness of the aquatic flora of Britain and Ireland, this work summarizes the distribution, habitat and reproductive biology of 200 taxa in 72 genera, and provides a brief summary of their wider distribution. Distribution maps are provided for all taxa, and each genus is illustrated with a line drawing to aid identification.