Two series of cationic dimeric ((gemini)) surfactants are presented with respect to key surfactant properties, such as surface activity and micellization. The influence of the dimerization and of the spacer group are examined, in order to establish structure-property relationships. Importantly, the addition of organic anions strongly modifies the solution properties and aggregate morphology. The surface tension and critical micellar concentration can be markedly reduced compared to the dimeric surfactants in the pure state. Moreover, dimeric surfactants with an appropriate spacer group can produce viscoelastic solutions after addition of certain organic anions even when bearing only dodecyl chains, whereas no effect is observed for such mixtures involving the analogous (monomeric) surfactant. Also, first results on the use of polymerizable counterions and their polymerization in such mixtures are presented.