The development of flexible and wearable electronics has grown in recent years with applications in different fields of industry and science. Consequently, the necessity of functional, flexible, safe, and reliable energy storage devices to meet this demand has increased. Since the classical electrochemical systems face structuration and operational limitations to match the needs of flexible devices, novel approaches have been in the research spotlight: gel polymer electrolytes (GPEs). Combining comparable ionic conductivity with liquid electrolytes with desirable mechanical stability, GPEs have been investigated in various electrochemical applications in sensors, actuators, and energy storage. This versatile class of quasi-solid material finds applications in the different components of energy storage devices. They are being investigated as electrodes, binders, electrolytes, and stand-alone systems due to desirable physical-chemical characteristics such as a wider potential operational window and high adhesion to solid electrode materials. Coalescing a liquid phase occluded into an entangled 3D polymeric matrix, these materials withstand elevated mechanical stress such as strain and compression, and they are also interesting materials for various applications. Moreover, they allow further functionalization to match the specific requirements of various energy storage systems. In this review, we summarize different applications of GPEs in energy storage devices, highlighting many valuable properties and emphasizing their enhancements compared to classical liquid electrochemical energy storage systems.