The deposition of nickel on polycrystalline aluminum substrates has been studied at room temperature by X-ray photoelectron spectroscopy (XPS), angle-resolved X-ray photoelectron spectroscopy (ARXPS), and valence band X-ray photoelectron spectroscopy (VBXPS). The growth of the nickel on the aluminum surface has been found to occur in two stages: Formation of NiAlx (x approximate to 0.45) islands 10 ML thick up to a coverage theta (NiAlx) = 0.7, followed by the formation of metallic nickel islands with constant thickness of 8 ML that grow over the intermetallic islands previously formed. The simultaneous lateral growth of both kinds of islands is also observed during the second stage. During the first stage, the VBXPS spectra suggest a net charge transfer from nickel to aluminum with the sequential formation of NiAl3, Ni2Al3, NiAl, and Ni3Al phases.