Molybdenum metal deposition from the decomposition of Mo(CO)6 adsorbed on Si(100), Mo, and Cu surfaces was studied by x‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy, thermal desorption spectroscopy, and low‐energy electron diffraction. Pyrolytic, photolytic, and electron‐induced Mo(CO)6 decomposition were observed and indicated different dissociation mechanisms. Thermally decomposed Mo(CO)6 was found to leave metallic Mo in the presence of C and O. Electron‐induced decomposition resulted in the formation of molybdenum carbide on the surfaces. Ultraviolet (UV) irradiation of adsorbed Mo(CO)6 induced new peaks in XPS and TDS spectra, suggesting the formation of an unsaturated molybdenum carbonyl adsorbate. Mo(CO)6 was found to form a multilayer on these surfaces at low temperatures, and desorb with zero‐order kinetics. Although both adsorbate desorption and decomposition took place when the samples were heated, desorption was the dominant reaction path. UV irradiation of gaseous and coadsorbed Mo(CO)6 and O2 was also investigated. UV irradiation of the gas‐phase mixture leads to MoO2 and MoO3 deposition; however, UV irradiation of coadsorbed Mo(CO)6 and O2 resulted in unsaturated molybdenum carbonyl. The effects of annealing and Ar+ bombardment on the Mo‐deposited Si(100) surface are also reported.