Electrochemical water splitting is a vital process for sustainable hydrogen production, yet its mechanistic pathways remain challenging to decipher due to the complexity of interfacial charge transfer and reaction intermediates. State-of-the-art electrocatalysts, primarily based on precious metals such as ruthenium, platinum, and iridium, exhibit excellent activity but suffer from high cost and scarcity, limiting their industrial scalability. Consequently, research has shifted toward alternative catalysts, including transition metal oxides, sulfides, phosphides, hydroxides, layered double hydroxides, and single-atom catalysts. These offer a promising balance of performance, cost, and abundance. Recent advancements in in-situ and operando characterization techniques, such as X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy, have significantly improved our understanding of catalytic dynamics under realistic reaction conditions. Complementary computational approaches, including density functional theory (DFT), provide atomic-level insights into reaction pathways and active site evolution. Despite these breakthroughs, challenges remain in capturing transient intermediate states and understanding structural transformations during long-term operation. This chapter integrates advanced experimental and computational methods to unravel the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) mechanistic pathways.