Recently, interest in batteries with high energy density has greatly increased as a result of the sharp rise in demand for electric vehicles, which are needed to achieve carbon neutrality by the year 2050. Lithium-sulfur (Li-S) batteries are emerging as the next-generation batteries owing to their high theoretical energy density of 2,600 W h kg-1. However, they are difficult to commercialize because of various hurdles, including the high reactivity of Li metal anode, shuttle phenomenon, and slow sulfur conversion reactions at the cathode. The development of advanced functional separators fabricated by coating functional materials on the surface of separators is one of the most promising strategies to tackle these issues and push Li-S battery performance to higher levels. The control of the physical and chemical properties of coating materials allows functional separators to exhibit multiple effects favorable for addressing the intrinsic issues of Li-S batteries, which is beyond the conventional role of general separators. Therefore, this review provides a comprehensive overview of the recent developments in functional separators for high-performance Li-S batteries.