Rechargeable lithium-sulfur (Li-S) batteries have recently attracted global research interest due to their high theoretical specific capacity and energy density. To improve the performance and cycling stability of Li-S batteries, a clear understanding of the electrochemical reaction process and the degradation mechanisms of the sulfur redox chemistry are extremely important. In the past few decades, various advanced in situ/operando characterization tools have emerged, which have facilitated the understanding of the degradation mechanisms and the further development of high-performance Li-S batteries. In this review, we have summarized recent significant advances in in situ/operando characterization techniques for Li-S batteries. In particular, because of the existence of the soluble polysulfide species during the charge/discharge process, many creative ideas have been introduced into in situ/operando characterization of the electrochemical process in Li-S batteries.