Adhesion and interfacial reactions at metal/polyimide interfaces have been studied using Auger electron spectroscopy (AES). Cr and Cu thin films were deposited on unmodified polyimide and in situ RF plasma-treated polyimide by conventional DC magnetron sputtering. Adhesion was measured by the 90 degrees peel test and interfacial reactions were characterized by Auger electron spectra obtained from peeled metal strips. Adhesion of the Cu film to polyimide was very weak, even with RF plasma treatment. While the peel strength of Cr to unmodified polyimide was low, the peel strength of Cr to RF plasma-treated polyimide was very high. AES analyses on the peeled metal surfaces showed that Cu does not react strongly with polyimide, but Cr reacts with polyimide to form a carbide-like phase and the RF plasma treatment increases this reactivity. Interfacial reactivity is directly related to the adhesion strength between the metal and the polyimide.