The goal of this study was to improve our understanding of diamond growth reactors. Direct relationships were set up between key parameters at a microscale level and diamond film characteristics. The coupled action of plasma variables, such as microwave power density, substrate temperature, and percentage of methane, on the density of the key species that control diamond growth was studied by spectroscopic diagnostics and modeling. The influence of local conditions on the domain of validity of the Van der Drift model, which describes texture development from a random distribution of diamond nuclei, is discussed. The results suggested that different chemical kinetic models, which depend on plasma conditions, must be used to describe "diamond" growth by chemical vapor deposition.