Dendritic growth of multiply branched InAs nanowires (see Figure and cover) is initiated by the controlled introduction of a Mn precursor in the context of vapor-liquid-solid nanowire growth by chemical vapor deposition. Self-assembly of Mn clusters leads to the nucleation and epitaxial growth of Mn-terminated InAs branches. The results provide a new route to the formation of hierarchical nanowire structures for nanoscale electronics and photonics.