Among the transition metal oxides, tungsten bronzes have attained considerable attention due to their chemical, electrical and optical properties which depend on the type of alkali-metal atom and its composition. The term tungsten bronze is applied to the non-stoichiometric compounds of general formula MxWO3 (0 > x > 1), where M is an alkali-metal atom. The common structural feature of these materials is the WO6 octahedra which are repeated along three directions through corner sharing. This structural arrangement provides various kinds of tunnels, which are at least partly occupied by alkali metal atoms. These materials undergo one or more structural phase transitions depending on the content of alkali metal x. The main part of this book is focused on LixWO3-PTB, in order to explore the stability field in the conventional solid state synthesis techniques and to investigate in particular their spectral properties. For polarised micro reflectivity, single crystals of LixWO3 are also prepared by chemical vapour transport method. The spectral and structural properties of Nb-doped and Mo-doped alkali metal tungsten bronzes, AxMyW1-yO3 (A = Li, Na, Cs and M = Nb, Mo) are also discussed.