Phthalate oxygenase catalyzes the oxygenation of phthalate to form a cis-dihydrodiol. It is comprised of two proteins: a flavo-iron-sulfur protein with NADH-dependent oxidoreductase activity (POR) and a nonheme iron protein with oxygenase activity (PO). The latter is a tetramer of 48 kDa units and contains a Rieske [2Fe-2S] center and one mononuclear iron per monomer. The mononuclear iron is likely the site of oxygenation. This system can be isolated in large quantities and is sufficiently stable for detailed mechanistic studies. We briefly describe some of our studies on this system which include kinetics, and visible, magnetic resonance, EXAFS, and ENDOR spectroscopies.