Due to the low reactivity of CH bonds and often low regio- and stereoselectivities, CH activations rank among the most challenging reactions in synthetic organic chemistry. In contrast, in nature CH functionalizations are integral part of numerous biosyntheses, especially of secondary metabolites. In aerobic organisms these reactions are typically catalyzed by oxygenases, among which the cytochrome P450 monooxygenases are the most prominent. A second large group are the a-ketoglutarate- (aKG) dependent dioxygenases, whose enormous synthetic potential has been discovered only recently. Although the utilization of oxygenases for organic synthesis is most desirable, their technical application is limited, because they are usually difficult to process. With aKG-dependent dioxygenases some of the problems can be reduced or even avoided. In this article some prominent examples for approaches with aKG-dependent dioxygenases are reviewed and efforts to engineer a deacetoxycephalosporin synthase are discussed.