Polymer nanocomposites is a combination of polymer matrix and with a wide range of 1-D, 2-D or 3-D filler materials (organic and inorganic) having at least one dimension in nm range. Polymer nanocomposites have unique structures, morphology as well as mechanical, thermal and electrical properties. Therefore, study on polymer nanocomposites are being continued for about 25 years. The transition from micro- to nano- particles lead to change in its physical as well as chemical properties. Carbonaceous nano fillers such as graphene, CNTs play a very promising role due to their better structural and functional properties such as high aspect ratio, high mechanical strength, high electrical properties etc. Several researchers have been able to successfully implement graphene or hybrid filler based polymer nanocomposites in electrochemical applications, lithium ion batteries, sensors, solar cell, water purification, supercapacitors, drug delivery and tissue engineering. Nanotechnology has the potential to create many new materials and devices with wide-ranging applications, such as in medicine, electronics, and energy production.