This E-book deals with Gas sensing, which is one of the most dynamic and technologically diverse sectors of the overall sensor industry. Today's products exploit numerous solid-state, electrochemical, optical and other phenomena and are used in a multitude of industries, including automotive, chemicals and petrochemicals, mining, food, defence and security, healthcare, water, power generation, oil and gas and others. They control processes, protect workers from hazards, prevent fires and explosions, monitor air quality in the external and indoor environments, analyse human breath, characterise odours and fragrances, reduce pollution and detect leaks and process malfunctions. The global research effort continues to expand and involves all manner of technologies, principles and materials. In addition to the body of work exploring the capabilities of new materials and phenomena, key practical objectives are the development of gas sensors with characteristics such as reduced power consumption, greater specificity, higher sensitivity, lower costs and reduced size, and the ability to monitor different gases simultaneously, operate in ever-more extreme environments and detect compounds that cannot be sensed with existing technologies.