Electrochemical energy storage in batteries and supercapacitors underlies portable technology and is enabling the shift away from fossil fuels and toward electric vehicles and increased adoption of intermittent renewable power sources. Understanding reaction and degradation mechanisms is the key to unlocking the next generation of energy storage materials. This chapter will highlight the diverse applicability and chemical sensitivity of solid-state NMR as a tool for studying bulk and interfacial structures and dynamics. NMR interactions relevant to inorganic battery and supercapacitor materials will be described before moving into sections on lithium battery cathodes, anodes, solid electrolytes, interfaces, and finally supercapacitors. While battery materials vary in maturity, each section focuses on materials that are either in commercial use or development. Multinuclear NMR studies of mechanisms, atomic structure, and ion dynamics are succinctly described and an effort is made to summarize the state of the field for each class of materials.