Exposure to light of intensity I =1.12 × 10 15 to 7.0 × 10 15 photons/(cm 2 s) at λ = 360 nm and T = 293 K produces significant changes in the absorption and reflection spectra and weight of indium films 1 to 32 nm in thickness. Kinetic curves for the photochemical transformation of the indium films are adequately represented by a linear, inverse logarithmic, parabolic, or logarithmic rate law. We have measured the contact potential difference across the In and In 2 O 3 films and the photovoltage in the In-In 2 O 3 system. A model has been proposed which includes the generation and redistribution of nonequilibrium charge carriers in the In-In 2 O 3 interfacial field, oxygen adsorption, In 3+ diffusion, and In 2 O 3 formation.