The quintessence of the hot-injection method, a synthesis route for monodisperse, highly luminescent semiconductor nanocrystals, is reviewed. The separate stages of nucleation and growth of the nanocrystals are discussed in the framework of classical nucleation theory and an equilibrium model proposed by Debye. We also review the numerous adaptations of the original synthesis that currently provide colloidal nanocrystals with well-defined, size-dependent optical, electrical, and magnetic properties. The availability of these remarkable materials is one of the most promising developments in nanoscience and nanotechnology.