This paper deals with homogeneous and heterogeneous primary nucleation and the atomistic model of heterogeneous primary and secondary nucleation. Three aspects of crystal growth mechanisms will be taken into account: growth by two-dimensional nucleation, the so-called birth and spread model, spiral growth without and with consideration of the influence of diffusion, and finally adhesive growth. An equation for the estimation of the growth rate of imperfect crystals including dislocations, published by Mersmann [1], is discussed. The influence of additives on nucleation and crystal growth, respectively, will be exemplarily explained for several model systems. The effect of growth rate dispersion (GRD) is described. Therefore, some experimental results concerning growth rates and different ways to influence growth are represented and discussed. Furthermore, a model explaining the effect of GRD is represented.