Nanogels, composed of swollen nano-sized networks of hydrophilic or amphiphilic polymer chains, are promising drug delivery carriers. They can spontaneously absorb biologically active molecules through various interactions and have a high loading capacity. Polyelectrolyte nanogels can incorporate oppositely charged low molecular mass drugs or biomacromolecules, leading to a significant reduction in nanogel volume. The collapse of nanogels upon drug loading results in stable nanoparticles, which remain dispersed due to the lyophilizing effect of hydrophilic polymers like poly(ethylene glycol). Nanogels can be modified with targeting groups for site-specific drug delivery and can release drugs in response to environmental cues such as pH or temperature. Recent studies have demonstrated the potential of nanogels in delivering phosphorylated nucleoside analogs, oligonucleotides, siRNA, and proteins for anticancer and antiviral treatments, as well as in encapsulating bioactive proteins and fabricating nanometallic or nanoceramic composites. The unique properties of nanogels, including their swelling and collapse behavior, responsiveness to environmental factors, and ability to load and release drugs, make them a versatile platform for drug delivery and imaging applications.Nanogels, composed of swollen nano-sized networks of hydrophilic or amphiphilic polymer chains, are promising drug delivery carriers. They can spontaneously absorb biologically active molecules through various interactions and have a high loading capacity. Polyelectrolyte nanogels can incorporate oppositely charged low molecular mass drugs or biomacromolecules, leading to a significant reduction in nanogel volume. The collapse of nanogels upon drug loading results in stable nanoparticles, which remain dispersed due to the lyophilizing effect of hydrophilic polymers like poly(ethylene glycol). Nanogels can be modified with targeting groups for site-specific drug delivery and can release drugs in response to environmental cues such as pH or temperature. Recent studies have demonstrated the potential of nanogels in delivering phosphorylated nucleoside analogs, oligonucleotides, siRNA, and proteins for anticancer and antiviral treatments, as well as in encapsulating bioactive proteins and fabricating nanometallic or nanoceramic composites. The unique properties of nanogels, including their swelling and collapse behavior, responsiveness to environmental factors, and ability to load and release drugs, make them a versatile platform for drug delivery and imaging applications.