Nanowires are nanostructures that have a thickness or diameter constrained to tens of nanometers or less and an unconstrained length. In addition, many different types of nanowires exist, including metallic, semiconducting and insulating. This book presents current research in the study of the properties, synthesis and application of nanowires. Topics discussed include semiconductor nanowires and heterostructure based gas sensors; transport properties of nanostructured materials; nanowire array electrodes in biosensor applications and analogies between metallic nanowires and carbon nanotubes