Seawater intrusion (SI) is a global issue exacerbated by increasing freshwater demand in coastal zones and rising sea levels. This review summarizes current SI research, compares methods for assessing and managing SI, and identifies future research needs. SI research is categorized into processes, measurement, prediction, and management. Over 50 years of research has provided various techniques for SI investigation, but knowledge gaps remain, particularly regarding transient SI processes and regional freshwater-saltwater interface characterization. Multidisciplinary research is needed to understand SI interactions with submarine groundwater discharge, ecosystem health, and unsaturated zone processes. Recent advances in numerical simulation and calibration require rigorous application to climate change, sea-level rise, and socioeconomic factors. SI process understanding is based on numerical simulations and laboratory experiments, but field-scale processes are poorly understood. Current SI research involves interdisciplinary approaches, including hydrogeochemical processes, and well-documented case studies are essential. SI processes include dispersive mixing, tidal effects, density-driven circulation, and saltwater upcoming. Heterogeneous aquifers influence SI through preferential flow paths and transport mechanisms. SI in heterogeneous systems is influenced by aquifer heterogeneity, leading to complex mixing zones. Sea-level fluctuations affect SI through tidal and storm events, with significant impacts on coastal hydrology. Hydrochemical processes in SI include carbonate dissolution, cation exchange, and sulfate reduction, altering water quality and hydraulic properties. Upcoming below wells is a result of pumping, causing saltwater to rise and reducing the freshwater zone. SI measurement involves head measurements, geophysical methods, and environmental tracers. Geophysical methods like resistivity and electromagnetic techniques are effective for mapping subsurface salinity. Environmental tracers help identify salinity sources and processes. Future research should focus on improving SI understanding, measurement, and management to address global challenges.Seawater intrusion (SI) is a global issue exacerbated by increasing freshwater demand in coastal zones and rising sea levels. This review summarizes current SI research, compares methods for assessing and managing SI, and identifies future research needs. SI research is categorized into processes, measurement, prediction, and management. Over 50 years of research has provided various techniques for SI investigation, but knowledge gaps remain, particularly regarding transient SI processes and regional freshwater-saltwater interface characterization. Multidisciplinary research is needed to understand SI interactions with submarine groundwater discharge, ecosystem health, and unsaturated zone processes. Recent advances in numerical simulation and calibration require rigorous application to climate change, sea-level rise, and socioeconomic factors. SI process understanding is based on numerical simulations and laboratory experiments, but field-scale processes are poorly understood. Current SI research involves interdisciplinary approaches, including hydrogeochemical processes, and well-documented case studies are essential. SI processes include dispersive mixing, tidal effects, density-driven circulation, and saltwater upcoming. Heterogeneous aquifers influence SI through preferential flow paths and transport mechanisms. SI in heterogeneous systems is influenced by aquifer heterogeneity, leading to complex mixing zones. Sea-level fluctuations affect SI through tidal and storm events, with significant impacts on coastal hydrology. Hydrochemical processes in SI include carbonate dissolution, cation exchange, and sulfate reduction, altering water quality and hydraulic properties. Upcoming below wells is a result of pumping, causing saltwater to rise and reducing the freshwater zone. SI measurement involves head measurements, geophysical methods, and environmental tracers. Geophysical methods like resistivity and electromagnetic techniques are effective for mapping subsurface salinity. Environmental tracers help identify salinity sources and processes. Future research should focus on improving SI understanding, measurement, and management to address global challenges.