Supercapacitors have attracted significant attention as energy storage devices owing to their high power density, high charging rate, and long cycle life. However, they possess low energy density, which limits their practical applications. To address this issue, various high-capacitance materials, such as transition metal oxides and conducting polymers, have been investigated. Recent pioneering studies have described the emergent pseudocapacitance in twodimensional (2D) nanomaterials, which are of significant interest because of their unique structure, remarkable physical properties, and tunable surface chemistry. Through this brief review, we present our contributions to this new class of pseudocapacitive 2D nanomaterials: oxidized black phosphorous, transition metal dichalcogenides, and MXene. The surface-capacitive charge storage mechanism of 2D nanomaterials is understood through in situ spectroscopic and computational analyses. Moreover, the corresponding capacitive features and performances are maximized by nanostructuring, nanoarchitecturing, and compositional control.