The common name mussel is used for members of several families of clams or bivalvia mollusca, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or oval. This book presents current research in the study of mussels and their anatomy, habitat and their environmental impact. Some of the topics discussed herein include the use of mussels as a reliable tool for monitoring marine pollution; mussel glue and its use in biotechnology; environmental impact to mussels' metabolism; the competition for space and food among Blue Mussels; the life cycle assessment of mussel culture; Unionidae freshwater mussel anatomy; and the cytogenics of Mytilus mussels.