This book presents the research results on the optical, sensory, and photocatalytic properties of hybrid nanocomposites with applications focused on optical and sensor studies and presents the unique techniques of synthesis and microstructure analysis of functional nanocomposites. Some results covered in this edition are devoted to structural changes upon interaction with the light, also sensitivity and selectivity during electrochemical systems. Some articles deal with analysing the use of MOFs' unique optical and sensory properties, nanostructured rare earth metal oxides, and inorganic nanocomposites in real sensor structures. Most of the research results are first reported, and the book will be helpful to specialists in sensor engineering, optoelectronics, and photocatalysis.