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.