Aqueous zinc-ion batteries (ZIBs) have attracted significant interest as safe, low-cost, and environmentally friendly energy storage systems. However, their performance and stability are limited by complex interfacial phenomena such as zinc dendrite growth, parasitic side reactions, and the evolution of the solid electrolyte interphase. These processes are inherently dynamic and span multiple spatial and temporal scales, posing challenges to traditional ex situ characterization techniques. To address this, advanced in situ and operando techniques have been developed, broadly categorized into imaging, spectroscopic, synchrotron scattering/diffraction, and coupled mass spectrometry approaches. These methods enable real-time visualization and chemical analysis of the electrode/electrolyte interface, providing insights into nucleation and dissolution dynamics, interfacial chemical transformations, and the mechanisms driving dendrite formation and parasitic reactions. Through the integration of these complementary techniques, structural evolution can be correlated with electrochemical behavior, elucidating the underlying physicochemical mechanisms. This review systematically summarizes recent advances in in situ and operando characterization methods and highlights their contributions to understanding interfacial stability in aqueous ZIBs. Future directions emphasizing multi-modal strategies and data integration to guide the rational design of high-performance ZIBs are discussed. These insights are expected to accelerate the development of next-generation aqueous energy storage systems.