The authors of this book examine polyethers and polyethylene glycol. The first chapter in particular gives a systematic, balanced and comprehensive summary of the main aspects of photosensitive polyethylene glycol. The second chapter is a focus on the biodegradation of polyethylene glycols (PEGs) and polyethoxylated surfactants. The third and last chapter of this book focuses on polyethylene glycol based phase change polymers for thermal energy storage applications. Life nowadays is often centered around technologies, and it is of utmost important to have the primary and secondary resources ready for present and future needs. This last chapter addresses these concerns and various procedures in which thermal energy can be stored and used.