Flow Capacitive Deionization (FCDI) has emerged as an innovative electrically driven separation technology with distinct advantages over conventional desalination methods. Utilising flowable carbon electrodes and ion exchange membranes, FCDI enables continuous operation, high water recovery, and selective ion removal at relatively low energy consumption. This review critically examines the historical development, operational mechanisms, cell architectures, and configurations of FCDI systems, with particular focus on recent advances in materials, flow-electrode formulation, and regeneration strategies. This review also highlights emerging opportunities for FCDI in selective ion recovery and resource extraction. Despite its promise, FCDI remains at a pre-commercial stage due to high capital costs and system complexity. Ultimately, progress in advanced materials, system modelling, and scalable cell design will be essential to realise its transition from laboratory innovation to a commercially viable solution for sustainable water treatment.