The nucleation of Ag and Au on alkali halides is discussed excluding the influence of adsorbed gas layers. In particular, the problems of nucleation density and of the orientation of nuclei with respect to the substrate crystal are treated. The influence of defects in the surface on nucleation density is discussed in detail. Some principal aspects necessary for a theoretical treatment are pointed out. A review of the problem of the orientation of nuclei is given. An explanation of some recent results, the possible influence of electrical double layers (Debye-Frenkel layers) in the surface region is discussed.