The generation of dendrimers is a powerful tool in the control of the size and biodistribution of polyion complexes (PIC). Using a combinatorial screening of six dendrimers (18–243 terminal groups) and five oppositely charged PEGylated copolymers, a dendrimer‐to‐PIC hierarchical transfer of structural information was revealed with PIC diameters that increased from 80 to 500 nm on decreasing the dendrimer generation. This rise in size, which was also accompanied by a micelle‐to‐vesicle transition, is interpreted according to a cone‐ to rod‐shaped progression in the architecture of the unit PIC (uPIC). This precise size tuning enabled dendritic PICs to act as nanorulers for controlled biodistribution. Overall, a domino‐like control of the size and biological properties of PIC that is not attainable with linear polymers is feasible through dendrimer generation. PIC and choose: The size and biodistribution of polyion complexes (PICs) can be hierarchically tuned with the generation of a dendrimer component in a way not attainable with linear polymers.