The applications of potassium ion batteries (KIBs) require the development of advanced electrode materials. The rate performance and cycle stability of anode materials are critical parameters and are closely related to their K⁺ storage mechanisms and structural changes during cycling. This review presents an overview of the electrochemical performance and energy storage mechanisms of currently widely studied anodes for KIBs, including carbon-based, alloy-based, and organic-based anodes. This mini-review covers the emerging operando protocols that are applied to the in-depth mechanistic study of the KIBs, and we hope it will provide guidelines for the design of advanced anodes for KIB technology and hence accelerate the commercialization of KIBs as competitive energy storage devices.