Surface-attached polydicyclopentadiene (pDCPD) films were prepared on gold and silicon substrates-via surface-initiated ring-opening metathesis polymerization (SI-ROMP) of dicyclopentadiene (DCPD). The films were grown utilizing monomer in both the vapor phase and the solution phase with the former process exhibiting rapid kinetics,producing similar to 400-nm-thick pDCPD films in less than 1 min of polymerization. No significant differences in thickness were observed for films grown from monomer in the vapor phase with the different isomers (exo and endo) of DCPD. Decane was used as an inert additive to control the concentration of DCPD monomer in the vapor phase enabling the preparation of pDCPD films with thickness ranging from tens of nanometers to hundreds of nanometers. The thickness of pDCPD films polymerized using monomer in the vapor phase was enhanced by the presence of a rinse solvent on the surface of the ROMP-active gold substrates. The choice of ROMP catalyst was found to be an important consideration when SI-ROMP was conducted on different substrates. Electrochemical impedance spectroscopy was used to reveal that the films provide effective barriers to the diffusion of aqueous ions in excess of 1 X 10(6) Omega.cm(2). The mechanical properties of the surface-tethered pDCPD films were quantified with AFM PeakForce quantitative nanomechanical mapping (QNM) with a measured reduced Young's modulus (E-r) of 15 GPa. The measured Er was greater than that of a non-cross-linked surface-tethered polymer, pNB, indicating that the pDCPD films are stiffer.