The growth morphology and electronic properties of Al films on Pt(111) have been investigated by STM, XPS and AES at 160 K and 300 K. Film growth is kinetically controlled at both temperatures, with formation of 2D Al dendrites during the initial stages of deposition. At 300 K, completion of the first monolayer is followed by 3D island formation, while at 160 K layer-by-layer growth persists for Al coverages ≥ 5 monolayers. Pt core-level and valence-band X-ray photoelectron spectra show growth of a high binding energy interfacial Pt state during 300 K deposition, indicative of Pt Al surface alloying. No significant alloying occurs during 160 K growth. At 300 K, deposition of second-layer Al signals the onset of adatom place exchange with the underlying Pt, reflecting a rather delicate balance between surface energy and free energy of alloy formation. The limiting Pt Al surface alloy stoichiometry corresponds to Pt 2Al 3, and the associated Pt core level shift is in quantitative accord with an interesting linear correlation which is found between the composition and associated core-level shifts of other Al-transition metal alloys.