Carbohydrate- and phenolic-based biopolymers have received great attention due to their natural biocompatible, biodegradable, nontoxic, and inexpensive properties. Hydrogel particles derived from natural polymers with size dimensions on the micrometer and nanometer scales (microgels/nanogels) are attractive as drug delivery vehicles because of their high surface area and tunable size range with different chemical functionalities. The release kinetics of active agents from microgel/nanogel carriers are controllable by adjusting properties such as the type and amount of cross-linker used and by making them responsive to various stimuli. The most widely investigated stimuli for controlled drug release include pH, solvent, electric fields, magnetic fields, ionic strength, and temperature. In this chapter, the preparation of stimuli-responsive biopolymeric microgels/nanogels for drug delivery application is focused by exploring the most recent literature. Biopolymeric microgels/nanogels prepared from carbohydrates such as hyaluronic acid, chitosan, carrageenan, dextran, inulin, carboxymethyl cellulose, and sucrose are discussed. Also, polyphenolic compounds such as quercetin, rutin, and tannic acid that are recently employed in microgel/nanogel particle preparation as controllable active agent-release vehicles and as drug carriers will be explored. Polyphenolic-based microgels/nanogels can release phenolic compounds, which possess antimicrobial, antioxidant, anticancer, antiallergic, and antiinflammatory properties upon degradation triggered by various environmental stimuli such as pH, temperature, solvent, specific molecule, or enzyme. The size, morphology, and bioactive properties of microgels/nanogels can be altered by changes in their preparation techniques, imparting various functional groups with tunable degrees of cross-linking between the biopolymeric chains. Therefore, the control of these parameters is the most imperative cue to design long-term sustained drug delivery systems.