Electrodeposition mechanisms of CuInSe2 thin films from SCN− baths were studied by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The formation of CuInSe2 was confirmed to proceed via the induced codeposition mechanism at more positive potentials than where Cu+ or In3+ alone are reduced. The reaction probably proceeds via Cu2−xSe formation because no InySe compounds could be deposited at the potential range where CuInSe2 formation was observed. The slope of the Δf vs. ΔQ plot corresponding to the CuInSe2 formation decreased during the cyclic voltammogram until it settled to a constant value which suggests that the compound formation begins on the previously formed Se film and that the deposition mechanism changes during the cyclic voltammogram when the Se film becomes covered with the compound. A wide potential range was observed where the slope of the Δf vs. ΔQ plot was constant. Film deposition at constant potentials also yielded essentially equal slopes.