Batteries using potassium ions as the charge carrier to store energy operate via different electrochemical processes and have different features of materials electrochemistry compared to lithium-based batteries. Thus, battery technologies based on electrochemical potassium storage exhibit different performance strengths, potentially having diverse market applications. This is particularly important for the search for environmentally and economically sustainable alternatives to conventional lithium-ion batteries in a wide range of applications. This book presents the state-of-the-art development of potassium-based batteries and in-depth discussion on their structure-to-performance relationships.