Polymers are the preferred insulating materials for several electrical applications due to their ease of production, light weight, and low cost. However, their low thermal conductivity constitutes a bottleneck and efforts are made in order to increase it. An approach to improve heat transfer through polymers is the inclusion of fillers with relatively high thermal conductivity. Investigation in this direction has been carried out by different research groups. In this paper, a reference to a number of different studies is made and the role of fillers in polymers is investigated. The main goal of this review is to determine any potential trends which govern and dictate the process of thermal conduction in polymeric composites including nanocomposites and microcomposites.