For the major scientific laboratories around the world, nanotechnology has been one of the key scientific issues since the end of the last millenium. The basic materials of this newly emerging technology are nanoparticles, which, in fact, have been used for many centuries. However, the physical properties of the particles were understood quite recently. In order to apply the new properties we have to protect and functionalize the surfaces of the particles, since without protection of the surfaces, nanoparticles grow themselves due to Ostwald Ripening. In this review, the author describes recent technical progress in the field of fuctionalization of various nanoparticles and their applications, so that readers can grasp the overall picture of this new technological field.