Quantitative characterization of uniform density, electrochemically inert films on electrodes is achieved by cyclic voltammetry (CV) of a redox probe that partitions from electrolyte into the film. Electrochemically inert films generate no faradaic current in the voltammetric window of the probe. In simulation models, probes pre-equilibrate into films, electrolyze at electrodes, diffuse in film and solution, and extract across film solution interfaces. Film thickness is I. Diffusion length 8 approximates distance from the electrode where voltammetry perturbs probe concentration; delta proportional to v(-1/2) for scan rate v. At high v, delta < l and voltammetric morphologies are typical of semi-infinite linear diffusion. As v slows, delta greater than or similar to l and CV morphologies can change with relative probe flux in the film and solution. For higher solution flux, voltammograms assume sigmoidal (S-shaped) characteristics; higher film flux generates gaussian (thin layer CV) characteristics. For film and solution diffusion coefficients D-f and D-s and kappa the equilibrium ratio of probe concentration in film to solution, diagnostics yield kappa root(D-f/D-s) and l(2)/D-f. Because diagnostics apply for all v, films are fully parameterized by CV alone. Without these diagnostics, full characterization requires a second, steady state voltammetric measurement. Diagnostics are vetted with [Ru(bpy)(3)](2+) (probe) in inert polymer films of Nafion and of poly(styrenesulfonate). (C) 2013 The Electrochemical Society. All rights reserved.