The process of crystal nucleation is modeled by two competing, the Classical (1) and the Balanced Nucleation and Growth (2, BNG), models. Both start with the formation of agglomerates from the reactant(s). The major practical outcome is the concept of the critical nucleus. From here, the two models take different paths. The well known classical model (1) attempts to model the nucleation rate, J (no/sec*cm3). This nucleation rate, J, is considered constant during the nucleation phase. On the other hand, the Balanced Nucleation and Growth (2, BNG) model focuses on the total number of stabile crystals formed, Z (no). Here, the nucleation rate (no/sec) varies during the nucleation phase and ends at a given time when only crystal growth is observed. During the nucleation phase the crystal number and size distribution is determined. The crystal number, Z, is a function of the maximum growth rate of the critical nuclei, the crystallization efficiency, the reactant addition rate, and the critical nucleus size. The BNG model consequently leads to an explicit, factor free model which quantitatively relates the number of crystals formed to reactant addition rate, crystal solubility, temperature, and the effects of crystal ripeners and growth restrainers. The consequences of these models on the process of practical crystallizations will be discussed.