AbstractSodium‐ion batteries (SIBs) as economical, high energy alternatives to lithium‐ion batteries (LIBs) have received significant attention for large‐scale energy storage in the last few years. While the efforts of developing SIBs have benefited from the knowledge learned in LIBs, thanks to the apparent proximity between Na‐ions and Li‐ions, the unique physical and chemical properties of Na‐ions also distinctly differ themselves from Li‐ions. It is expected that SIBs have drastically different electrode material structure, solvation–desolvation behavior, electrode–electrolyte interphase stabilities, ion transfer properties, and hence electrochemical performance of batteries. In this review, the authors comprehensively summarize the current understanding of the anode solid electrolyte interphase and cathode electrolyte interphase in SIBs, with an emphasis on how the tuning of the stability and ion transfer properties of interphases fundamentally determines the reversibility and efficiency of electrochemical reactions. Through these carefully screened references, the authors intend to reveal the intrinsic correlation between the properties/functionalities of the interphases and the electrochemical performance of batteries.