A feasible mechanism for catalyst‐ and template‐free InN nanorod growth was proposed, consisting of the random nanoparticle nucleation from stable gas phase oligomers and the subsequent directional growth along the c‐axis. A combined study of equilibrium analysis and computational thermochemistry was used to determine the optimal growth conditions – growth temperature and Cl/In ratio – for InN nano‐rod growth based on the proposed mechanism, and the computationally determined values showed a good agreement with reported experimental results. The involvement of InCl3 as a key species in the proposed mechanism required the Cl/In ratio to be ∼ 3 by stoichiometry. The growth zone of InN nanorods by HVPE was demonstrated to lie in the vicinity of the growth‐etch transition. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)