This dissertation discusses several of the many applications of polyaniline nanofibers and composites. Polyaniline is a conducting polymer which has been used for decades, however only within the past few years has it become a processable material with the development of polyaniline nanofibers and dispersions. The nanofibrillar morphology allows one to use polyaniline easily. The processability and high surface area allow efficient use in applications such as sensors, artificial muscles, metal nanoparticle scaffolds, bistable memory devices, electrochromics, water purification, capacitors and many other areas. Improved control of the synthesis of polyaniline, its derivatives, and other conducting polymers promise an even greater enhancement of the application range for these lightweight and inexpensive materials.