Cleavage of C-O and C-N bonds mediated by transition metals is a promising bioorthogonal approach to rescue the activity of caged molecules, such as proteins and cytotoxic drugs, under biological conditions. However, the precise mechanism of such uncaging reactions remains elusive. This review provides mechanistic insights into metal-mediated bond-cleavage reactions, with the goals of understanding the main factors that influence the reaction and aiding the rational development of new caging groups/catalysts for chemical biology and drug-delivery applications.