 Biodegradable nanoparticles, NPs, are increasingly being investigated for their potential use as carriers for delivering vaccines, genes, drugs, and other biomolecules into the body. These particles offer improved biocompatibility, superior drug, vaccine encapsulation, and convenient release profiles for a range of drugs, vaccines, and biomolecules. This paper reviews the methods of preparation of biodegradable NPs, the factors affecting optimal drug encapsulation, the factors affecting drug release rates, the surface modifications of nanoparticles to enhance in vivo circulation, and the specific applications such as tumor targeting, oral delivery, and delivery of these particles to the central nervous system. This article was offered by Mahapotro Anil and Singh Dinesh K.