Among various devices for removing submicrometer particles from a gas stream, fibrous filters have the advantages of providing high collection efficiencies at low-pressure drop. Even in the absence of electrostatic forces. a fibrous filter captures particles efficiently by inertial impaction, interception, and convective Brownian diffusion. Application of electrostatic forces can significantly increase the efficiency of collection. The process of aerosol filtration in the presence of electrostatic forces is complicated. Although past studies have led to a good understanding of the filtration process in clean filters, there is a marked gap between theory and experiment of the change in collection efficiency with particle loading in a filter in the presence of electrostatic forces. This paper gives a review on both theoretical and experimental studies on the application of electrostatic forces in filtration and discusses the needs for further studies on the effect of particle loading.