Electrospinning of composite nanofibers has been attracting great attention as a way of producing functional nanofibers. Composite nanofibers are produced with the incorporation of the additives into the polymer melt/solution before electrospinning process and reported to show many superior properties such as high modulus, increased strength, improved thermal stability, or some new functionalities such as flame retardancy, antimicrobial properties, water repellency, soil resistance, decreased gas permeability, electromagnetic shielding, electrical conductivity, and so on. The availability of the wide range of additives makes it possible to produce a wide range of functional nanocomposite nanofibers that are promising for various applications. Polyaniline (PANI) as an inherently conductive polymer is being investigated as an additive for improving conductivity. Carbon nanotubes (CNT) are widely used for either their reinforcement ability or their superior electrical conductivity. Silver nanoparticles (AgNPs) are being incorporated into polymer matrices to obtain antibacterial activity. This chapter provides a comprehensive review about polyacrylonitrile (PAN) nanofibers with PANI, CNTs, AgNPs, and their combinations and highlights the synergistic effects obtained by their combined use.