Nanotechnological application is greatly important in the field of drug delivery because of its high specificity towards the target site, so it is able to reduce toxic side effects of drugs to normal cells. Reduce plasma fluctuation of drugs, high solubility, efficiency, reduces cost of products and enhancement of patience comfort are reasons that nanotechnology is used for drug delivery. The nanoparticle (NP) plays a vital role and it can conjugate with various drugs by different methods to deliver drugs to the target site. The NP surface is designed with ligands to get affinity towards specific cells and co-polymers to get protection from immune cells. The nanoparticles conjugated drug can eventually recognize the site and join to the target and enter to the cell by receptor mediated endocytosis. Then NPs are able to release drugs controllably to cure diseases. This review analyses the nanotechnology in drug delivery, discovery, nanoparticles and formulation, mechanism of drug delivery and applications.