X-ray diffraction, high-resolution electron microscopy, and 57Fe Mössbauer spectroscopy have been used to study the WO 3Fe system. The results from the diffraction methods can be interpreted either on a scheme involving bronze formation leading to a phase Fe xWO 3, or on a scheme whereby a reduced tungsten oxide is in equilibrium with FeWO 4. The Mössbauer results show, however, that up to x = 0.0193 in Fe xWO 3, a bronze is formed with either an orthorhombic or tetragonal structure, while above x = 0.0193 the phases are FeWO 4 and reduced tungsten oxides. The Fe xWO 3 bronze contains a few isolated (102) crystallographic shear planes, which implies a very slight deviation from the ratio WO 3. Reaction of Fe with WO 3 or FeWO 4 with WO 3 and W at 950°C under vacuum leads to the bronze phase.