Wet etching is commonly used to produce patterned copper films for printed circuit boards and semiconductor devices. The investigation of copper etching by FeCl3-HCl solutions in a batch stirred-tank reactor was undertaken to determine the intrinsic reaction kinetics. The variation of the etch rate with FeCl3 concentration was linear at low concentrations and gave first-order rate constants of 0.2039, 0.3083, and 0.3362 mg Cu.kg H2O/cm2.s.mol FeCl3 at 30, 40, and 50-degrees-C, respectively. At approximately 2 mol/kg the etch rate reached a maximum. Etch rates obtained with 0.85 and 2 mol/L HCl over the range of FeCl3 concentration were similar. The etch rate was substantially reduced with the use of Fe(NO3)3-HNO3 solutions and increased uniformly as the chloride content of the solution was increased. Concentrations of the chloro complexes of the iron(III) ion were computed and showed that FeCl2+ and FeCl3(0) are the principal species present in the etchants studied. The etch rate was found to vary linearly with FeCl2+ concentration at low (<1 mol/kg) concentrations. The maximum in the etch rate is attributed to the inhibition by FeCl3(0), the concentration of which becomes significant in etchants of greater than 2 mol/kg FeCl3.