Sodium metal anodes have attracted significant attention due to their high specific capacity (1166��mA h g���1), low redox potential (���2.71��V vs the standard hydrogen electrode), and abundant natural resources. Nevertheless, unstable solid electrolyte interphases (SEI) and uncontrolled dendrite growth critically hinder their commercialization. Notably, SEIs play a critical role in regulating Na deposition and improving the cycling stability of rechargeable Na metal batteries. Recently, SEI research on Na metal anodes has been intensively conducted worldwide; thus, a comprehensive review is necessary. Herein, initially, the fundamentals of SEI and the related issues induced by its intrinsic instability are discussed. Thereafter, advanced characterization techniques that unveil the morphological evolution and interfacial chemistry of Na metal anodes are presented. Subsequently, efficient strategies, including liquid electrolyte engineering, artificial SEI, and solid-state electrolyte technology, to stabilize SEI��films are outlined. Finally, key aspects and prospects in the development of SEI for Na metal anodes are highlighted. It is believed that this review will serve to further advance the understanding and development of SEIs for Na metal anodes.