Vanadium has been reported to be an essential bio-element for certain organisms, including tunicates, bacteria and some fungi. This book aimed to describe the coordination chemistry of vanadium with biologically relevant ligands and presents synthesis of oxo, dioxo and oxoperoxovanadium(V) complexes. Most common oxidation states are +IV and +V and generally stabilized through V?O bond. Oxocations [VO]2+, [VO]3+ and [VO2]+ are most common for biological systems. The development of structural and functional model complexes of vanadium haloperoxidases is the key motive of vanadium chemistry and some of the complexes can be considered to be structural models of haloperoxidases. The model character also extends to functional similarities, in that they catalyse the oxidation, by oxidant, of sulfoxide, styrene, cyclohexene, phenol, trans-stilbene etc. Vanadium complexes have also been found to catalyze the oxidation and epoxidation of various organic substrates. Some of the complexes have also been tested for their antiamoebic activity.