Chemical sensors contain two basic functions: recognition and transduction, and provide real-time information about substances rather than physical quantities. Such devices are extensively utilized for various applications in diverse fields. The book focuses on the physical, chemical, optical, and electrical working mechanisms of different types of sensors integrated with various smart nanomaterials and composites. The mesmerizing properties of numerous materials and their fruitful applications for detecting numerous chemical parameters are discussed here. The book provides recent progress in the chemical sensors field and connects materials, physics, chemistry, and engineering, and therefore, is suitable for engineers, industrial, and academic researchers.