Nanoalloys of gold and platinum show special chemical qualities. As catalysts, for example, they are superior to pure Au and Pt nanoparticles under rather different experimental conditions. We demonstrate that combining Au and Pt leads to an advantageous combination of properties: The Pt component contributes a high density of states close to the Fermi level, which can promote chemical activity. The Au component increases the atomic mobility, which can allow the particles to structurally adapt to different chemical situations and adsorbates. Special catalytic properties of Au-Pt nanoparticles are thus expected based on general considerations, that is, inherent properties of the Au and Pt component, respectively.