The renaissance of Li-S battery technology is evidenced by the intensive research efforts in recent years. Although the theoretical capacity and energy of a Li-S battery is theoretically very high, the projected usable energy is expected to be no more than twice that of state-of-the-art Li-ion batteries, or 500 Wh/kg. The recent “sulfur fever” has certainly gathered new knowledge on sulfur chemistry and electrochemistry, electrolytes, lithium metal, and their interactions in this “old” system; however, a real advance toward a practical Li-S battery is still missing. One of the main reasons is the lacking of fundamental understanding of Li-S batteries at cell levels. The surface/carbon composite, their particle size, sulfur electrode porosity and density critically dictate the deliverable energy from Li-S chemistry, whereas the parasitic reactions on Li metal anode determines the cycling life of the cell. This talk will briefly overviews the recent research progress on Li− S batteries, followed by a discussion of the scientific gap between lab research and realistic conditions of cell fabrication. The future work in Li-S battery research is also explored to propel relevant research efforts to accelerate the market penetration of Li-S batteries.