This literature review discusses the sludge formation in the Hall–Héroult process. Sludge formation and its transformation into resistive cathodic deposits is one of the focal concerns of the aluminum producers. Sludge formation interacts with the complex dynamics of the electrolysis cells while increasing the energy demand and decreasing the current efficiency. The data on such important phenomenon are scattered through years in proceedings of TMS Light Metals and journal articles; hence, requiring an in-depth review including the influence of important parameters such as temperature (i.e., superheat), bath chemistry, cathode type, alumina feeding characteristics, hydrodynamics, and interfacial phenomena.