Semiconductor “quantum dots” refer to nanometer-sized, giant (103–105 atoms) molecules made from ordinary inorganic semiconductor materials such as Si, InP, CdSe, etc. They are larger than the traditional “molecular clusters” (~1 nanometer containing ≤100 atoms) common in chemistry yet smaller than the structures of the order of a micron, manufactured by current electronic-industry lithographic techniques. Quantum dots can be made by colloidal chemistry techniques (see the articles by Alivisatos and by Nozik and Mićić in this issue), by controlled coarsening during epitaxial growth (see the article by Bimberg et al. in this issue), by size fluctuations in conventional quantum wells (see the article by Gammon in this issue), or via nano-fabrication (see the article by Tarucha in this issue).