Cadmium (Cd) is a toxic heavy metal of increasing environmental concern due to its wide variety of adverse effects. Living organisms are exposed to Cd through the intake of food, water and contaminated air. Cadmium is absorbed from the gastrointestinal tract and the lungs, and is mainly accumulated in the liver and kidney where it is bound to metallothionein (MT). When Cd concentration exceeds the binding capacity of MT, the non-bound Cd causes toxicity possibly due to free radical induction and lipid peroxidation. This book emphasises how the Cd relation to the antioxidant system and other elements enhances our understanding on the role of Cd in the environment.