The increasing of pollution by heavy metals in last decades has focused attention on the behavior of these metals in aquatic ecosystem, Biomarkers have considered as valuable tools in Biomonitoring of pollution by heavy metals, Biomarkers can be define as any biochemical, Molecular, Histological and physiological changes according to environmental stress .This book includes different measurements of Biochemical markers such as antioxidant,Metallothionein,Acetylcholinesterase, Molecular Biomarkers such as DNA damage and protein profile, and Histological markers in selected Molluscs to evaluate pollution by heavy metals,the measurement of previous biomarkers is so important to give early warning signals for pollution, this book is so significant for University lecturers,postgraduate and undergraduate students in Environmental Biotechnology Field.