Presented here are keys and notes on distribution and ecology for the freshwater snails (Gastropoda), mussels (Unionidae), and fingernail clams (Sphaeriidae) which have been collected from the Laurentian Great Lakes. Including subspecies and forms, 121 taxa are discussed: 47 Gastropoda, 39 Unionidae, and 35 Sphaeriidae. Relations to substrate preferences and pollution are summarized where known. Special emphasis is given to the sphaeriid genus Pisidium in discussions of morphological variability and characters which will separate the species and forms both in the adult and immature stages. Both drawings and scanning electron microscope photomicrographs are presented for all sphaeriid taxa. A limited synonymy has been compiled from publications and reports on the Laurentian Great Lakes and the expanded reference section includes not only citations used in the text but also publications and reports which may aid researchers in more indepth studies of the fauna.