Classically, a sample of any bulk material exhibits two obvious length scales: the first is simply its macroscopic size, and the second, less-obvious one is a nanometer periodicity that is due to the lattice structure of the component atoms or other underlying constituents. K. H. Muller and colleagues recently quantified the bulk conductivity of a coated nanocrystal assembly, in terms of the individual particle sizes, the parallel conduction routes, and the barrier thickness. In this case, the conductivity is controlled by the barrier thickness (coating thickness) and the number of barriers per unit length. This chapter summarizes some of the key synthetic improvements and breakthroughs in the creation of different core–shell nanocrystals. It presents a survey of several procedures that have allowed the encapsulation of metal, semiconductor, and magnetic nanocrystals with metal oxides, as well as the main advantages that have thereby been acquired.