The advancement of nanotechnology in drug delivery has revolutionized cancer therapy, particularly through the development of nanogels as promising drug carriers for targeted and “On-demand” controlled drug delivery. Nanogels are nano-sized hydrogel particles formed via physical or chemical cross-linking, display remarkable adaptability due to their ability to incorporate various functionalities. This adaptability enables surface modifications with targeting moieties, allowing for site-specific active cancer targeting. Furthermore, incorporating specific molecular functionalities transforms conventional nanogels into innovative smart stimuli-responsive systems. These surface-engineered nanogels can respond to internal biological stimuli such as pH, enzymes, temperature, ROS, and redox conditions, and external stimuli such as magnetic fields, light, and ultrasound. This stimuli-responsive behavior is mainly beneficial in cancer therapy, as it ensures site-specific controlled drug release, suppressing off-target drug toxicity and enhancing therapeutic efficacy. For instance, pH-responsive nanogels exploit the acidic microenvironment condition of tumors for selective drug release, while redox-sensitive systems leverage intracellular differences in oxidative states. Moreover, these carriers can encapsulate a variety of therapeutic agents, including chemotherapeutics, genetic molecules, and immunotherapeutics, offering a multimodal approach to cancer treatment.