Nanogels are three-dimensional nanosized networks that are formed by physically or chemically cross-linking polymers. They have been explored as a drug-delivery system due to their biocompatibility, high stability, particle-size adjustment, drug-loading capability and modification of the surface for active targeting by cognate receptors on the target cells of tissues. Nanogels can respond to stimuli such as pH, temperature, light and redox, which results in the controlled release of drugs and targeting of site by environmental stimuli and prevents accumulation in non-target tissues, minimizing the side effects of the drug. This book aims to provide a general introduction to nanogels and the design of various stimuli-sensitive nanogels that can control drug release in response to specific stimuli.