The lithium-sulfur battery (LSB) is a promising next-generation technology for vehicle electrification because it exhibits higher theoretical specific capacity and specific energy density than the current state-of-art lithium-ion battery. LSB electrochemistry mainly involves a series of redox reactions over the intercalation mechanism of lithium-ion batteries. However, LSB reactions and operations are complex owing to multistep redox kinetics and a solid-liquid interface reaction. Therefore, starting with a brief cell history, this chapter introduces LSB electrochemistry and presents the fundamental understanding of electrochemical reactions occurring within the cells and their operational mechanism based on the current state of the art in LSB literature. © 2022 Elsevier Inc. All rights reserved.