It is of great interest to the energy community to understand how the mechano-physico-chemical phenomena that eventually lead to device degradation are related to the startup, operation, and shutdown phases. For electrocatalytic systems operating in liquid electrolyte environments, the understanding of these phenomena at each stage can pave the way for the tailored design of efficient and commercially viable electrocatalysts. Transmission electron microscopy plays an important role in the investigation of local electrocatalytic effects, complementing other operando characterization techniques. Herein, after attempting to define the meaning of operando methodologies in relation to electron microscopy studies, the progress in the field is reviewed in terms of the knowledge gained about the catalysts, the solid -liquid interfaces, and the solid -liquid -gas interfacial phenomena for several electrocatalytic reactions. Finally, the parameters that require consideration in quasioperando ec-LPTEM studies of electrocatalytic systems are discussed.