The transition to sustainable energy demands efficient and durable catalysts for the oxygen evolution reaction (OER), which represents the kinetic bottleneck in water electrolysis. This chapter provides a comprehensive overview of recent progress in the design, mechanisms, and structure—property relationships of metal oxide electrocatalysts for OER. The discussion begins with the mechanistic fundamentals involving proton–electron-coupled steps and lattice oxygen participation, followed by the establishment of standardized evaluation metrics, including overpotential, Tafel slope, faradaic efficiency (FE), and electrochemically active surface area. The major classes of oxides single-metal oxides, spinels, perovskites, layered double hydroxides, and complex oxides such as pyrochlores and Ruddlesden–Popper (RP) phases are systematically analyzed to reveal how crystal structure, electronic configuration, and oxygen-vacancy chemistry govern catalytic activity and stability. Design strategies encompassing nanostructuring, multimetal synergy, defect and strain engineering, and interface modulation are highlighted as powerful tools for enhancing intrinsic performance. Finally, challenges related to acidic durability, neutral-pH operation, and scalability are addressed, emphasizing the integration of operando characterization, data-driven modeling, and descriptor-guided discovery. Together, these insights provide a unified framework for developing next-generation oxide catalysts capable of meeting the combined requirements of activity, stability, and cost for industrial OER applications.