Mammalian iron(II)- and 2-oxoglutarate-dependent (Fe/2OG) dioxygenases have roles in oxygen and body-mass homeostasis, connective tissue synthesis, and control of transcription and epigenetic inheritance. Related enzymes in plants, fungi, and bacteria enable and diversify biosynthetic pathways to valuable natural-product drugs by catalyzing halogenation, epimerization, desaturation, cyclization, ring-opening/expansion, and endoperoxidation reactions; an important subset of these enzymes even catalyze multiple reaction types in sequence. Almost every enzyme in this class initiates its reaction by decarboxylating 2OG to succinate to drive formation of a largely conserved oxoiron(IV) (ferryl) intermediate, first demonstrated by the Penn State group in 2003. This potently oxidizing intermediate cleaves C–H bonds to initiate the impressive array of outcomes mentioned above. The enzymes that mediate an outcome other than hydroxylation must avoid what can be a facile coupling of the substrate radical with the iron-coordinated oxygen that abstracted the hydrogen, a step known as "oxygen rebound." By direct biophysical observation and "metallomimicry" of intermediates, we have rationalized several of these outcomes in terms of the alternative fates of the substrate radical and the structural features of the enzyme that direct these fates. Recent work on less well-understood reaction types raises the possibility of previously unrecognized, novel control strategies, as I will outline in my presentation.