Among the various groups of aquatic insects, mayflies (Ephemeroptera) are of special interest for professional limnologists, entomological researchers, naturalists, and even the dedicated fly angler. Traditionally, identification has been considered difficult. Implementation in environmental monitoring and freshwater management has led to an ever increasing demand for exact information on taxonomy and ecology. This book provides an up-to-date reference for Ephemeroptera identification, including last instar larvae (nymphs), subimago (dun), and male and female imagines. Recent changes in nomenclature are discussed in detail. Keys are provided for genera and introductory chapters characterize every family and genus. Species accounts follow a common format, providing a synonymy, characters for identification (including literature references), remarks (on type material, variation, confusing or extralimital species), and information on biology and distribution patterns. Male genitalia are illustrated by micrographs and line drawings. REM photographs of the egg chorionic structure are provided for genera and selected species. Habitus of larvae and imagines are, for most genera, illustrated by color photographs. The geographical area covered is Europe, including the European part of Russia, the Mediterranean islands, as well as North Africa. Additional information is provided for adjacent parts of the western Palaearctic Region. A comprehensive index, check list, and distribution catalogue (following the widely adopted concept of Illies' Limnofauna Europaean) allow for quick information on all species recorded so far in Europe.