This talk will describe the synthesis, characterization, and electrocatalytic properties of dendrimer-encapsulated nanoparticles (DENs). DENs are prepared in two steps. First, appropriate metal ions are complexed to dendrimer templates. Second, the resulting complex is reduced. This results in nearly monodisperse metal nanoparticles containing 30-240 atoms. Slight alterations of this general procedure yield bimetallic DENs having alloy or core/shell structures. The characterization of such small materials presents some interesting analytical challenges that will be discussed. Finally, the electrocatalytic properties of monometallic and bimetallic DENs will be described. Because of the small size of the encapsulated nanoparticles, their electrocatalytic properties can be predicted using first-principles calculations.