In recent years, there has been a resurgence of interest in supercapacitors as high-power electrical energy storage devices with complementary properties to batteries. However, despite their growing applications in new technologies, many fundamental aspects of the charging mechanism remain poorly understood. Recently, some of the fundamental questions about supercapacitors have started to be addressed due to the emergence of NMR spectroscopy as a powerful tool for studying ion behavior in porous carbon electrodes. This chapter provides an overview of NMR methods that have been developed for the study of supercapacitors and reviews recent applications. These span both conventional NMR methods which have been used to study the equilibrium adsorption behavior as well as more advanced in situ methods which have begun to provide insight into working devices.