Core/shell nanoparticles (NPs) are formed using various strategies and offer considerable advantages for diagnosis and therapy. Because of the hydrophilic nature of their shell with relatively small size, core/shell NPs have been utilized to solubilize hydrophobic drugs as well as imaging agents, improving pharmacokinetics. This chapter will introduce various types of core/shell NPs based on their preparation method and formation mechanism. The focus will be on the core/shell nanomedicine for tumor targeting, stimulated release of proteins, and cancer imaging capabilities.