This document summarizes research on the structure and phase behavior of Cu-Ni nanoalloys. It uses thermodynamic modeling to predict how the phase diagrams and mixing/demixing behavior depend on nanoparticle size, shape, and temperature. The modeling indicates Cu-Ni nanoalloys can form either mixed particles or Janus particles, depending on the synthesis temperature, with nickel preferentially segregating to surfaces. Phase maps are provided to guide experimentalists on controlling particle structure.