Catalytically grown carbon nanofibers are novel materials that are the product of the decomposition of carbon-containing gases over certain metal surfaces. Studies in our laboratory have demonstrated that the structure and properties of the fibers can be tailored by careful control of a number of parameters including the nature of the metal surface, the composition of the gas-phase reactant, the temperature, and the incorporation of either gas-phase or solid additives. High-resolution transmission electron microscopy studies have revealed that the nanofibers consist of well-ordered graphite platelet structures, the arrangement of which can be engineered to desired geometries by choice of the correct catalyst system. When the data from these examinations are combined with the information of the associated catalyst particle morphology, it is possible to develop models that describe many of the structural characteristics as well as some previously unknown mechanistic features of the various carbon nanofiber conformations.