Several environmental contaminants including toxic trace metals are being discharged into the coastal environment causing serious threat to marine organisms and posing public health risk. Marine bivalves (mussel, oyster, and clam) have been successfully used as sentinel organisms for monitoring contaminant levels, including trace metals, in coastal waters around the globe. Chemical analyses measure the contaminants present in the biota but do not necessarily reveal potential biological effects. Therefore, the need to detect and assess the effects of contaminants, especially at low concentrations, has led to the development of molecular markers of contaminant effects called biomarkers.Owing to their short time of response, biomarkers in marine bivalves are used as early warning signals of biological effects caused by environmental pollutants. Research into the development and application of accurate biomarker-based monitoring tools for the environmental contaminants has been intensified in several developed countries.