This thesis entails the development of practical and cost-efficient deuteration methodologies. The first C–H activation and deuteration of aromatic substrates using an earth-abundant manganese catalyst and transient directing groups was reported. Secondly, the transient directing group strategy was transferred to a ruthenium-catalyzed hydrogen isotope exchange reaction. Lastly, the electronic characteristics of pyridine derivatives were harnessed for a transition metal-free deuteration protocol. The results are expected to inspire future developments in sustainable hydrogen isotope exchange.