This is the first book to specifically focus on semiconductor nanocrystals and address their synthesis and assembly, optical properties and spectroscopy, and potential areas of nanocrystal-based devices including applications in biology and medicine. Nanoscience will transfer into new products and processes in the next two decades. One emerging area where this challenge will be successfully met is the field of semiconductor nanocrystals. Also known as colloidal quantum dots, their unique properties have attracted much attention in the last twenty years. These highly efficient fluorophores have a strong band-gap luminescence tuneable by size as a result of the quantum confinement effect and are particularly interesting for applications in biology as luminescent labels. Control over a nanocrystals size at the synthetic stage is a straightforward way to obtain materials with designed optical properties. Applications of nanocrystals in photonics, optoelectronics and biotechnology are currently envisaged.