Seawater intrusion (SI) is a significant global issue, exacerbated by increasing freshwater demands in coastal areas and influenced by rising sea levels and changing climates. This review provides an overview of the current state of knowledge in SI research, compares methods for assessing and managing SI, and identifies areas for future research. The review is divided into categories related to processes, measurement, prediction, and management. Despite extensive research spanning over 50 years, there are still knowledge gaps in understanding transient SI processes, particularly in highly heterogeneous and dynamic settings. Multidisciplinary research is needed to evaluate interactions between SI and submarine groundwater discharge, ecosystem health, and unsaturated zone processes. Recent advances in numerical simulation and calibration techniques require rigorous field-scale application to address climate change, sea-level rise, and socioeconomic and ecological factors. The review highlights the importance of well-documented case studies and intensive measurement campaigns to accurately characterize interfaces and their movement in response to real-world coastal aquifer stresses. The complexity of SI processes, including dispersive mixing, tidal effects, density effects, and anthropogenic influences, necessitates a multidisciplinary approach to understanding and managing SI.Seawater intrusion (SI) is a significant global issue, exacerbated by increasing freshwater demands in coastal areas and influenced by rising sea levels and changing climates. This review provides an overview of the current state of knowledge in SI research, compares methods for assessing and managing SI, and identifies areas for future research. The review is divided into categories related to processes, measurement, prediction, and management. Despite extensive research spanning over 50 years, there are still knowledge gaps in understanding transient SI processes, particularly in highly heterogeneous and dynamic settings. Multidisciplinary research is needed to evaluate interactions between SI and submarine groundwater discharge, ecosystem health, and unsaturated zone processes. Recent advances in numerical simulation and calibration techniques require rigorous field-scale application to address climate change, sea-level rise, and socioeconomic and ecological factors. The review highlights the importance of well-documented case studies and intensive measurement campaigns to accurately characterize interfaces and their movement in response to real-world coastal aquifer stresses. The complexity of SI processes, including dispersive mixing, tidal effects, density effects, and anthropogenic influences, necessitates a multidisciplinary approach to understanding and managing SI.