Two stacks of nanotube arrays are joined together, driven by the nanoscale Kirkendall effect. The background images show elemental mapping of copper and oxygen. The contrast of colors shown in the maps represents the intensity of the signals. Such mapping analysis reveals that the interface of the joined nanotubes is copper oxide. On page 2546, C. L. Gan and co-workers demonstrate that the transformation from Cu nanowire arrays into copper oxide nanotube arrays can be coupled with the joining of the stacked chips in a single step process. By controlling the environment, temperature, and duration, joined Cu2O or CuO nanotube stacked chips can be achieved, which serve as a platform for the further development of stacked nanostructured devices.