With sizes (1–5 nm) between simple ions and large colloids, solution behaviors of macroions cannot be described either by Debye-Hückel limiting theory or DLVO theory. In addition, the large size disparity between macroions and small counterions makes their self-assembly process even more complicated. With charges carried by macroions, electrostatic interaction usually plays a critical role during self-assembly. A well-known feature of these structurally well-defined macroions with moderate charges is the spontaneous formation of hollow, spherical, single-layered blackberry structures, whose size can be accurately controlled via pH, solvent polarity, and salt concentration, based on counterion-mediated attraction. These blackberry structures show some unique properties, e.g., unique kinetic properties similar to the virus capsid formation, self-recognition, chiral-recognition, and permeation of small counterions through their membranes. Based on the complex structures of macroions, various interactions, such as hydrophobic interaction, van der Waalsforces, hydrogen bonding, and cation-π interactions, can be involved to compete or cooperate with electrostatic interaction to tune their self-assembly behaviors.