This part reviews the structure of hydrogen-free tetrahedrally bonded amorphous carbon films. It starts with an overview on the corresponding structural characteristics and the methods for their determination by experiments or by simulations. The structures of ta-C films are discussed in their dependence on the sp3 content and in comparison to the structures of amorphous silicon and liquid carbon. The superficial top layers and ultrathin films show some structural pecularities. The influence of the deposition conditions, especially ion energy and substrate temperature, on the resulting film structure is presented. The corresponding empirical relations are the base for elucidation of the film formation. The growth process is presented as a combination of ion impact, short-time excitation with subsequent quenching and final relaxation. The various theoretical growth models are critically discussed.