Since the beginning of faunistic studies the class Bivalvia belongs to one of the best investigated groups in the North Atlantic region. in Germany there is also a long tradition concerning the research in this group of animals. Especially since the beginning of the 1990s, due to the increase of offshore activities associated with wind farms, gas pipelines and oil fields and the consequent need for environmental impact assessments, the demand for knowledge of benthic residents, their distribution and ecological needs has increased. There is more than one reason to present a new key book on bivalves for the German parts of the North Sea and Baltic Sea. First, it is an attempt to consider all marine species observed at least once in the whole catchment area. Altogether 123 bivalves species are listed for the German waters and are comprehensively pictured and described; their distribution is given in maps. Second, due to the rapid increase of non-indigenous species, we included species that seem to be in the process of becoming established as well as those that already are. The reader now has the opportunity to rely on one monograph rather than having to combine several well-known handbooks from neighbouring areas or to search in several publications dealing with a single species. Furthermore, another 18 species from the adjacent Kattegat are briefly described and illustrated. Another 43 species are known from the Skagerrak and are listed in a table with their water depth ranges. To complete the work, another recently arrived species was described and illustrated in the addendum. The total number of species covered in this book is 185.weiterlesen