In the last three decades there has been increasing interest in bioinorganic chemistry in general, and the structural and functional modeling of metalloproteins in particular. This chapter is concerned with manganese redox enzymes and their synthetic models. Of the ever-increasing number of manganese-containing biomolecules now recognized [1-15] a few are known to be redox in nature. These include manganese-containing superoxide dismutase (EC, catalase (EC, Mn-ribonucleoside reductase (EC, Mn-peroxidase, ligninase, the oxygen-evolving center (OEC) of photosystem II (PSII), and Mn-thiosulfate oxidase.