This book highlights emerging exposure of gas having toxic nature, which is currently a focus of research at laboratories around the world. First, the synthesis of undoped and doped ZnO thin films by the spray pyrolysis method has been described. Moreover, the physical characterizations by means of X-ray diffraction (XRD), atomic force microscopy (AFM) and optical spectrophotometry techniques of these films are made in terms of various doping transition metal elements: nickel, copper and vanadium. Second, the electrical conductivity of such doped films has been carried out under different temperatures. Finally, the films prepared using appropriate content of eatch doping element have been tested for gas sensing characteristics towards ethanol vapor.