A nanowire is a wire of diameter of the order of a nanometre (10-9 meters). Alternatively, nanowires can be defined as structures that have a lateral size constrained to tens of nanometres or less and an unconstrained longitudinal size. At these scales, quantum mechanical effects are important -- hence such wires are also known as "quantum wires". Many different types of nanowires exist, including metallic (e.g., Ni, Pt, Au), semiconducting (e.g., Si, InP, GaN, etc.), and insulating (e.g., SiO2,TiO2). Molecular nanowires are composed of repeating molecular units either organic (e.g. DNA) or inorganic (e.g. Mo6S9-xIx). The nanowires could be used, in the near future, to link tiny components into extremely small circuits. Usingnanotechnology, such components could be created out of chemical compounds. This book presents the latest research from around the world in this dynamic field.