Hybrid Nanoparticles (AHNs) are rationally-designed multifunctional nanostructures and novel building blocks for the next generation of advanced materials and devices. Nanoscale materials attract considerable interest because of their unusual properties and potential for practical applications. Most of the activity in this field is focused on the synthesis of homogeneous nanoparticles from metals, metal oxides, semiconductors, and polymers. It is well recognized that properties of nanoparticles can be further enhanced if they are made as hybrid structures. This program is concerned with the synthesis, characterization, and application of such hybrid structures termed AHNs. AHNs are composed of a homogeneous core and several caps of different materials deposited on its surface (Fig. 1). Combined properties of the core and the caps as well as new properties that arise from core-cap and cap-cap interactions render AHNs multifunctional. In addition, specific chemical reactivity of the caps enables directional self-assembly of AHNs into complex architectures that are not possible with only spherical nanoparticles.