The sol-gel optical pH sensors have wide range of applications into engineering, industrial and environmental fields. Sol–gel encapsulated materials usually have some limitations (e.g. suffer from leaching of the sensing agent and has longer response time). In this work, modified sol-gel optical thin films pH sensors were prepared using surfactants, with low leaching and shorter response time. This unique book summarizes the current knowledge of sol-gel technology to provide stable silica matrix as host material for pH indicators in different forms as monolithic discs and thin films. It covers all fundamental aspects of the sol-gel encapsulation of pH indicators together with analytical methods used for their characterization. This book includes four chapters, covers all aspects of using sol-gel technology to encapsulate pH indicators as pH sensors. It is a valuable concise book for MSc and PhD students, academics and industrial researchers who are working in this interesting field.