The chemical growth of bulk or nanometer-sized materials involves the process of precipitation of a solid phase from solution. The challenge in nanoparticles synthesis is to control the size and shape of the crystals such that their properties can be tailored. This requires the understanding and control of the key processes of nucleation, growth and termination. Many strategies are available: sol processes, micelles, sol-gel, hydrothermal syntheses, etc. Among the most common and widely studied semiconductor nanoparticles are those of the II-VI type (ZnS, ZnSe, CdS, CdSe, CdTe and HgS) and of the III-V type (e.g., GaAs, InP and InAs). Semiconductor NP can be prepared in aqueous media using stabilizing agents, with procedures similar to those employed for the synthesis of gold NP. These approaches, however, lead to highly defective and polydisperse nanocrystals. More recently, procedures have been reported for the synthesis of highly crystalline and nearly monodisperse NP. For example for CdE (E=S, Se or Te), Cd precursor (dimethyl Cd, Cd oxide, carbonate or acetate) is added with chalcogen (elemental S, Se or Te) and treated in a hot coordinating solvent (e.g., TOPO, tri-n-octylphosphine oxide). High temperature makes fast particle nucleation and low temperature creates slow particle growth. If the desired size is reached then reaction quenching is done fallowed by washing to get nanoparticles. If not the process goes back to low temperature step of slow particle growth.