Nanosized particles including nanovaccines are a novel approach to the development of vaccines to combat diseases. Nanovaccines have the promise to utilize the immune system to cure infections and to prevent infections and diseases from spreading. Rational vaccine development requires an understanding of vaccine mediated stimulation of the immune system. We review here immunostimulatory properties of nanovaccines including their immunogenicity, adjuvant properties, inflammatory responses and the mechanisms of uptake and stimulation of immune cells. Examples of various nanoparticles currently being developed as vaccines are also provided.