Tungsten oxide hydrates WO3 . nH(2)O are formed upon the acidification of tungstate aqueous solutions. Different amorphous or crystalline phases can be obtained depending on the experimental conditions (pH, concentration, temperature). The chemical mechanisms for the formation of these hydrates are discussed and the electrochromic properties of thin films deposited from these solutions are described. Hydrogen peroxide H2O2 reacts with tungstic acid H2WO4, leading to the formation of peroxo species. These new precursors are more stable preventing the rapid precipitation of WO3 . nH(2)O. Moreover, this process allows the formation of mixed WO3-TiO2 precursor solutions. Transparent amorphous thin films are deposited by spin or dip-coating. They exhibit longer lifetime upon coloration-bleaching electrochromic cycling.