Organic ionic plastic crystal composites exhibit properties that make them suitable for many applications including energy storage devices and CO2 separation. In most cases, the mixing of organic ionic plastic crystals with a polymer, salt or a porous material leads to the formation of interfacial regions that can enhance the ion transport of desired ions like Li+ for battery applications. The study of these interfacial regions is challenging and requires the use of spectroscopic techniques like solid-state NMR to characterise the structure, interactions, and ion dynamics. This article summarises the advantages and challenges of organic ionic plastic crystals and their composites, and the common NMR methods used to study the interfacial regions between their components.