Carbon filament, vapor grown carbon fibers and carbon nanotubes have been discovered to have remarkable properties, opening they way for their use in intriguing and novel applications in electronics, chemistry and materials science. There are many similarities between nanotubes and filaments, leading many researchers to critically compare the two materials, their production, and potential applications. The two materials are compared and contrasted in depth in the present book, which is a comprehensive review of current research activity, growth mechanisms, physical properties, industrial production, and applications. The structures are discussed using a unified approach, which helps to compare growth mechanisms, contrasting morphological differences, and detailing how novel properties depend on such differences.