This book by Dr. Sapana Rane & Dr. Suresh Gosavi highlights the new technologies, nano-crystalline materials along with thin or thick film technology. Hydrogen (H2) has experienced an increased interest around the world due to its potential as future renewable source of energy. However, massive hydrogen use requires extremely safe control systems in every gas involving process (production, manipulation and storage) to prevent any leakage (due to smallest atomic size) that might eventually produce an atmosphere of easy ignition. Hence accurate detection of hydrogen leakage is extremely important especially at or near room temperature with minimal power consumption and weight and with a low rate of false alarms. Along with this it is important to focus on reducing the response time of hydrogen leak detection. Thus there is a huge demand for reliable, inexpensive H2 gas sensors. The book thus gives an insight in preparation of metal-metal oxide based thin/ thick film sensors with good sensitivity, selectivity preferably for hydrogen (H2) gas with less response and recovery time, at preferably low or room temperature operating conditions. The book is useful for fellow students and researchers.