This chapter is devoted to the chelation treatment of transfusion-dependent thalassemia patients. After a brief overview on the pathophysiology of iron overload and on the methods to quantify it in different organs, the chelation therapy is discussed, giving particular attention to the chemical and biomedical requisites. The main tasks of an iron chelator should be the scavenging of excess iron, allowing an equilibrium between iron supplied by transfusions and that removed with chelation, and protection of the individual from the poisonous effects of circulating iron. The chelating agents in clinical use are presented, illustrating the main chemical and pharmacological features, together with a comparative cost analysis of their treatments. As a final section, an overview is provided on chelators undergoing clinical trials, and on research in progress.