Per- and polyfluoroalkyl substances (PFAS) are called forever chemicals due to the extremely stable C─F bond (bond energy of 485 kJ·mol), which leads the persistent existence in the natural environment thus poses a threat to human health. Compared with simple removal without destruction, defluorination is a more meaningful and thorough way for the harmless disposal of PFAS. In this review, the relationship between the structural properties of PFAS and defluorination mechanism are concluded. Thereafter, we discussed the advantages and limitations of defluorination techniques and specific defluorination pathways of active substances (free radicals and electron). This will provide a comprehensive theoretical foundation for the selection and improvement of defluorination technologies. The influence of key factors on the practical application of defluorination technologies in wastewater treatment plants are assessed in detail from the perspectives of reaction solvents, homogeneous and heterogeneous systems, and reactor design. Importantly, the pilot-scale application of relevant PFAS defluorination technologies has also been discussed. Finally, we prospect for the future research direction of PFAS defluorination from the aspects of precise exploration of reaction pathways, fluorine balance, resource recovery, and life cycle assessment (LCA). This will provide a practical strategy for addressing the urgent issue of PFAS-contaminated wastewater.