Our society requires gas sensors for domestic, automotive,industrial applications due to the implication of gases in environmental control or dangerous emissions. Metal oxide resistive gas sensors are used in monitoring toxic gases as they offer very high sensitivity and relatively long-term stability. To enhance the sensor behavior doped semiconductor oxides material is used. In this context the author’s contribution was to use the dopant like cobalt and molybdenum in noble material SnO2, which is the most extensively studied oxide for the sensor application. Its objectives were to develop a smart, mobile gas sensor system with low power consumption. For the synthesis spray Pyrolysis system has been used.To study the sensing characteristics towards detection of different gases and vapors,in air,compatible gas sensing systems were used. The author has investigated the influence of synthesis temperature, concentrations of precursor and dopant materials on gas sensing behavior in terms of the sensitivity, selectivity, response and recovery times. This book will help, who work on synthesis of thin films,especially using spray pyrolysis technique and the gas sensing characteristics.