The energy industry sector is vast, and nanotechnology has revolutionized and improved this field by making it more efficient, sustainable, and economical. Nanofillers, as the name suggests, are fillers having particle sizes in the nano range. The size of the fillers can have a profound impact on the material’s performance and properties. The nanoscale fillers have a very large surface area and aspect ratio, which immensely enhances properties such as electrical resistivity, chemical and catalytic reactivity, adhesion, storage, etc. This has attracted tremendous research, especially in the energy storage field, which led to the development of efficient solar cells, improved batteries and supercapacitors, and more durable fuel cells. The effect of materials such as carbon-based nanofillers and metal-oxide nanofillers in energy storage devices has been largely investigated and reported. There has been extensive research focused on 0D, 1D, and 2D nanofillers utilized in the advancement of energy storage devices; for instance, 1D nanofillers provide large dipole moments resulting in increased energy density and improved dielectric permittivity. There is considerable research reporting the performance of carbon nanofillers on the improvement of mechanical stability and thermal conductivity. Also, the addition of nanofillers increases the formation of phases, which are electroactive and polar in the matrix of polymer, which aid in upscaling of the usability of hybrid composite in energy storage applications. This chapter will discuss the advantages of nanofillers in dielectric capacitors. The different types of nanofiller used in dielectric capacitors and various aspects of nanofiller such as size, type, amount, level of dispersion, surface property, etc., influence the properties and performance of the hybrid nanocomposite, specifically highlighting the associated challenges, which are discussed in detail.