Of the approximately 4,200 species of mammals inhabiting the earth, few are singularly adapted for existence in wetland environments. Yet wetland habitats provide important resources for many mammals that occupy broad ecological niches but are typically associated with other habitat types. With an overall goal of seeking common trends, the specific purposes of this chapter are: (1) to review the importance of wetlands as habitats for mammals and (2) to discuss the contribution of mammals to wetland ecosystem dynamics.