Arsenic, the poison of Kings and the King of Poisons, is a relatively common element that occurs in both abiotic and biotic world. Besides its medicinal use, arsenic is an established environmental pollutant and its contamination due to both geogenic and anthropogenic activities in some blocks of West Bengal is a serious public health issue for last three decades. Arsenic has a high bioaccumulation rate causing moderate to severe tissue and intracellular damages. Though in general, protoplasmic poisons act by structurally modifying important cellular proteins but it has been proposed that toxic effect of arsenic depends mainly on functional modifications. This work has been designed to provide a general understanding of the nature and extent of cyto- and geno-toxicity of a Arsenic. This book should be especially useful to students of undergraduate postgraduate students, researchers, and common people who are interested in different aspects of this deadly poison.