The improvement of high-performance devices with advanced efficiency, sustainability, and reliability based on innovations in nanomaterials and nanotechnology has impacted the energy storage and conversion landscape. This chapter provides a comprehensive overview of the applications of nanomaterials and nanotechnology in various energy-related fields, including batteries, supercapacitors (SCs), fuel cells, and smart materials. The design, synthesis, and characterization of nanostructured materials with the highlights of their unique properties and advantages in energy storage and conversion were enumerated. Furthermore, types of nanomaterials, nanoparticles, nanotubes, and graphene as well as their use in energy storage devices, such as lithium-ion batteries and SCs, are explained. In addition, ethical issues, advantages, and prospects in this rapidly evolving field are stated, emphasizing the importance of nanotechnology to renew the energy landscape and maintain a sustainable future. A valuable resource for researchers working in the field of energy storage and conversion for further investigation should be available.