Coastal flooding threatens lives, infrastructure, ecosystems, and economic activity, making reliable assessments essential for coastal planning and adaptation to sea-level rise. Coastal flood assessments over regional to global scales must reconcile broad spatial coverage with the local processes that control hazardous water levels and inundation. This review examines the physical foundations and methodological approaches used in large-scale assessments, with particular attention to the representation of wave contributions to total water level. Six complementary method groups are considered: analytical and empirical formulations, physics-based numerical models, physical experiments, data-driven models, GIS and remote sensing, and in situ observations. Selected large-scale studies are critically assessed in terms of wave parameterization, coastal morphology, interactions among water-level components, and validation. The review identifies recurring limitations associated with uncertain foreshore slopes, the transferability of empirical relationships, simplified process interactions, and scarce observations of overtopping and inundation. It also highlights that improved offshore forcing does not necessarily yield more reliable shoreline hazard estimates, and that total water level alone cannot determine inland flood extent. A modular, tiered framework combining regional screening with targeted high-resolution modelling and independent validation offers a practical means of balancing coverage and local detail. Further progress requires improved topographic and bathymetric data, systematic flood-event observations, and uncertainty propagation throughout the assessment chain.