This literature review borrows from diverse fields because of the paucity of freshwater wetland studies on mercury cycling and effects. Peat cores provide an excellent means of dating mercury deposition temporal patterns. Conclusions about cycling suggest that a biogeochemical model would prove useful for evaluating wetland processes of mercury transformation and accumulation. Mercury methylation and the association of mercury with organic matter require additional research. Wetlands trap and release mercury, and its association with organic matter seems to affect the release rate. At high exposure, usually associated with laboratory studies or waste discharges, a variety of biotic toxic responses are observed. Predator species accumulate mercury predictably, and residue-effect relationships seem useful for an index of ecologic damage. More definitive conclusions require additional research to define the ecosystem properties that affect mercury transfer to wetland predators.