Supercapacitors, known as electrochemical capacitors, are very attractive as energy storage devices due to their high-power density (up to 410 kW kg−1), their unique ability to undergo charge/discharge quickly and their long cycling life (that could reach 4105 cycles). Efforts have been dedicated to develop various carbon-based nanomaterials for energy storage, specially supercapacitors. Carbon-based materials and conducting polymers (ie; Polypyrrole and Polyaniline) are considered the most promising candidates for capacitive materials, as they offer high charging capacity through diverse mechanisms. Among these carbon-based materials are nano-crystalline diamond (NCD) films, which were widely studied during the past decades due to their special features like; short-range sp3 bonded carbon atoms and large surface to volume ratio. Artificial fabrication of NCD films was developed using various techniques like; high-pressure high-temperature (HPHT), chemical vapor deposition, plasma-discharge-stimulated, laser ablation,hot-filament technique,, and coaxial arc plasma deposition. Although carbon-based nanomaterials display good stability in energy storage applications, the capacitance values are yet limited by the microstructures within the materials; Therefore, their nanocomposites with conducting polymers provide higher performance and improved properties. This chapter aims to summarize and discuss the recent synthetic developments of nanocrystalline diamond/conducting polymer nanocomposites, and their applications to energy storage and supercapacitor.