Abstract: An X-ray photoelectron spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED) investigation of the growth of Cu films on a Pd(1 1 1) single crystal at room temperature is presented. Dynamically taken XPS-data as function of the deposition time show a linear variation of ICu-3p/IPd-3d and a periodic change of its slope indicating a nearly layer-by-layer growth process. RHEED oscillations are seen for the 3-4 first layers, also suggesting a smooth growth mode. From the evolution of the RHEED-streaks separation the in-plane Cu-atom spacing is precisely determined. Up to a coverage of ca. 2-3 monolayers (ML) Cu grows pseudomorphously on Pd(1 1 1), despite the -7.1% strain imposed by the substrate lattice parameter. Non-pseudomorphous epitaxial growth is evidenced above ca. 3-4 ML by a discontinuous change in lateral lattice spacing observed by RHEED which indicates a relaxation to the Cu(1 1 1) ''natural'' surface lattice parameter. In addition it is concluded that surface alloying does not take place at least at room temperature (RT)-XPS spectra taken dynamically during annealing show that alloying occurs only above RT Ver menos