Publisher Summary The surface energy, the interfacial energy, is one of the most fundamental quantities in the elementary processes of particle formation, including the nucleation event, particle growth, Ostwald ripening, and coagulation. In a typical monodisperse particle system, the monomeric species are initially accumulated in the system through some reaction from a reservoir of the monomeric species involved in the system. In this stage, no appreciable nucleation occurs, even if the concentration of the monomeric species exceeds the solubility level of the bulk solid. When the concentration reaches a critical level for nucleation, the nucleation virtually starts to be observed. In this stage, the nucleation rate is rather low, so the concentration of the monomeric species continues to increase, though the increasing rate is a little lowered due to their consumption for nucleation. However, as the concentration still increases, the nucleation is drastically accelerated and, finally, the concentration of the monomeric species reaches the maximum level.