By using different mechanisms of deposition and growth, new models of Parylene deposition rates have been developed and compared with experimental data over a wide range of conditions. It is shown that the surface adsorption (boundary) condition is a crucial factor in determining how the results of these models behave. Minimal differences in the behavior of the overall rates of deposition are obtained among the Parylene models using the same adsorption condition with either surface or bulk film reactions. However, their basic structures are considerably different. Although both diffusion/reaction and surface reaction models with either Langmuir-type or Flory-type monomer adsorption have attractive features, they fail to represent the data on rates of deposition over the wide range of conditions reported in the literature. In contrast, the models based on Brunauer, Emmett, and Teller multilayer adsorption seem to include the benefits of both Langmuir and Flory adsorption and simulate the data well over a much broader range of temperature. This suggests that multilayer adsorption is an important phenomenon in the low temperature vapor deposition of these polymers. Here we try to clarify the important physical/chemical mechanisms involved as well as the similarities and differences among various approaches to formulation of deposition models. A polynaphthalene deposition model is developed on the basis of both gas phase reactions followed by adsorption on the surface with subsequent reaction to form the film. The model is capable of simulating the data very accurately. However, the data available are limited in range and more experimental data are required to establish the uniqueness of the rate equations proposed.