A review. Numerous catalytic H2O2-based oxidn. reactions by polyoxometalates (POMs) were developed. POMs for H2O2-based oxidns. can be classified into three groups from the standpoints of their structures and H2O2 activation properties: (a) di- and tetranuclear small peroxotungstates, (b) lacunary polyoxotungstates, and (c) transition-metal-substituted POMs. This chapter focuses on the activation of H2O2 from groups (a)(c) including reaction mechanisms. Recent progress in the selective oxidn. with H2O2 catalyzed by POMs is comprehensively summarized. [on SciFinder(R)]