Size control of monodispersed particles must normally be performed during the very short nucleation period, because the final particle number is determined by the end of the nucleation and it does not change until the end of the particle growth. On the other hand, the shape control is mainly performed by adsorption of shape controllers during the growth period, although in some cases the crystal structure of the nuclei may have essential influence on the morphology of the grown particles. The internal structure of each particle is often strongly affected by the action of shape controllers. This article deals with the fundamental mechanisms of the nucleation, growth, and structural formation of monodispersed nano- and micro-particles, leading to the control of their size, shape, and internal structure.