Polymers in the form of nanofibers are attractive candidates for use in sensor applications because of their functional properties, in particular high surface area and high fiber aspect ratio. Electrospinning has proven to be a simple, versatile, and scalable technique for fabricating polymer fibers in the size range of a few nanometers to a few micrometers. In the past few years, we have witnessed tremendous research progress in understanding electrospinning mechanisms in generating polymer nanofibers and their applications in various fields including sensors. In this chapter, the authors focus on how the electrospinning has been influenced in the processing of polymer nanofiber-based sensors and, as well as their recent developments. An overview of electrospinning technique, fabrication of polymer nanofibers, and applications of polymer nanofibers in sensors are briefly discussed to convey the current state of the art of electrospun nanofiber-based sensors - specifically chemical and biological sensors. © 2012 Scrivener Publishing LLC. All rights reserved.