Semiconductor and Metal Nanocrystals: From Nanoengineering and Nanoscience to Practical Nanotechnologies Victor I. Klimov Chemistry Division Los Alamos National Laboratory I will give an overview of our research on synthesis, characterization, and applications of nanoscale structures built from semiconductor and metal nanocrystals.Using colloidal nanochemistry, we fabricate nanocrystals of II-VI and IV-VI semiconductors with nearly atomic precision in a wide range of sizes and shapes. We can combine different semiconductors to produce complex multishell structures or fabricate hybrid, bi-functional nanocrystals comprising magnetic metals and semiconductors. Our broad-band, near-field extinction spectroscopic studies reveal a number of unusual physical behaviors arising from quantum-mechanical confinement of electronic excitations in individual nanoparticles and/or strong interfacial interaction between nanoparticles in assembled structures. New nanosize regime functionalities lead to new technologies, such as color-selectable nanocrystal lasing, energy-transfer-powered light emitting diodes, and carrier-multiplication enhanced solar cells.