Mononuclear non-heme ferrous iron dependent oxygenases and oxidases constitute an extended enzyme family that catalyze a wide range of oxidation reactions. The largest known sub-group employs 2-oxoglutarate as a cosubstrate and catalysis by these and closely related enzymes is proposed to proceed via a ferryl intermediate coordinated to the active site via a conserved HXD/E…H motif. Crystallographic studies on the 2-oxoglutarate oxygenases and related enzymes have revealed a common double-stranded β-helix core fold that supports the residues coordinating the iron. This fold is common to proteins of the cupin and the JmjC transcription factor families. The crystallographic studies on 2-oxoglutarate oxygenases and closely related enzymes are reviewed and compared with other metallo-enzymes/related proteins containing a double-stranded β-helix fold. Proposals regarding the suitability of the active sites and folds of the 2-oxoglutarate oxygenases to catalyze reactions involving reactive oxidizing species are described.