Abstract: Amidst escalating global energy demands and the environmental constraints of conventional fossil fuels, hydrogen energy has emerged as a pivotal zero-emission energy carrier. The four-electron oxygen evolution reaction (OER) exhibits slower kinetics compared to the two-electron hydrogen evolution reaction (HER), constitutes the limiting process in electrolytic hydrogen production, with two principal mechanisms currently understood to govern its kinetics: the adsorbate evolution mechanism (AEM), which typically exhibits high stability but relatively low activity in its conventional framework, and the lattice oxygen oxidation mechanism (LOM), which generally shows high activity but insufficient stability in pristine systems. Notably, recent advances in catalyst engineering have enabled the development of modified AEM/LOM-based catalysts that balance stability and activity. Recent mechanistic developments have broadened this paradigm with proposed oxide pathway mechanisms (OPM) and coupled oxygen evolution mechanisms (COM), which incorporate innovative concepts such as dynamic surface reconstruction and concerted proton–electron transfer processes. This review firstly reviews the OER mechanisms, including AEM, LOM, OPM, and COM, followed by a systematic enumeration of identification strategies based on the core features of each mechanism, including kinetic features, experimental features, and theoretical calculations. Finally, we further highlight emerging opportunities in mechanism-directed material innovation, offering actionable insights for next-generation sustainable energy technologies.