Electrochemical cells with high energy densities are of great importance to satisfy the urgent demand for electronic vehicles and electricity storage. The Li-S battery is one promising candidate, yet it suffers from the low utilization of active materials and poor cycle stability. The electrochemistry and challenges facing Li-S batteries is addressed, and recent progress of materials related to Li-S batteries is summarized. (Angew. Chem. Int. Ed., 2013, 52, 13186-13200)