Nanotechnology as defined by the National Nanotechnology Initiative (NNI) is the study and use of structures roughly in the size range of 1 to 100 nm. Nanoparticles render a promising drug delivery system of controlled and targeted drug release. Nanoparticles are defined as particulate dispersions or solid particles with a size in the range of 10-1000 nm. The drug is dissolved, entrapped, encapsulated or attached to a nanoparticle matrix. Depending upon the method of preparation, nanoparticles, nanospheres or nanocapsules can be obtained. Nanoparticles specially designed to release the drug in the vicinity of target sites. In this article we discuss about nanoparticles and its evaluation parameters.