A new room-temperature, aqueous solution-based preparation method for chalcopyrite CuInSe2 has been developed. Using 10% aqueous ethylenediamine as a solvent, the slow addition of Cu(NO3) 2 to a mixture of indium(III) acetate, elemental Se, and sodium thioglycolate results in the formation of CuInSe2 as characterized by Raman spectroscopy. During this reaction, a kinetically-stable Cu 2-xSe(s) intermediate initially forms followed by slow conversion to CuInSe2 that likely involves a direct Cu2-xSe + In 2Se3 solid-state reaction. The ethylenediamine in the reaction mixture acts as a complexing agent, establishing equilibria that can be in competition with Cu2-xSe(s) formation, limiting particle size and accelerating rates of reaction with In. Over several hours, the CuInSe 2 material undergoes a phase decomposition that can be reversed by annealing at 550 °C. Attempts to prepare CuIn1-xGa xSe2 and CuGaSe2 via this method result primarily in CuInSe2 and Cu2-xSe products, respectively, with nearly all gallium staying in the solution phase.