The uranyl ion, [(UO2)-O-VI](2+), possesses rigorously trans, strongly covalent, and chemically robust U-oxo groups. However, through the use of anaerobic reaction techniques, both one- and two-electron reductive functionalization of the uranyl oxo groups has been discovered and developed. Prior to 2010, this unusual reactivity centered around the reductive silylation of the uranyl ion which entailed conversion of the oxo ligands into siloxy ligands and reductive metalation of the uranyl oxo with Group 1 and f-block metals. This review surveys the large number of new examples of reductive functionalization of the uranyl ion that have been reported since 2010, including reductive borylation and alumination, metalation with d- or f-block metals, and new examples of reductive silylation. Other examples of oxo-group functionalization of [(UO2)-O-VI](2+) that do not involve reduction, mainly with Group 1 cations, are also covered, along with new advances in the photochemistry of the uranyl(VI) ion that involve the transient formation of formally uranyl(V) [(UO2)-O-VI](+) ion.