This Account describes research in organic chemistry and materials chemistry, research which is focused on a specific type of intermolecular bonding between the π-systems of ion radicals. Our strategy was to study ion radicals in solution and to use this knowledge to develop and understand electrically conducting polymers. We discovered an unusual phenomenon, the formation of π-stacks in solution, and developed some understanding of the molecular qualities which promote this phenomenon. These stacks are interesting because π-electrons are delocalized among the molecules in the stacks, sometimes leading to electrically conducting materials. In fact our studies led to the invention of new conducting polymers, such as the first conducting dendrimers, and polymers with unusual humidity-dependent and highly anisotropic (directional) conductivity. Studies of oligomer cation radicals in solution have also implicated π-aggregates as structural features in conducting polymers such as oxidized polythiophenes. These aggregates are important for understanding how electrons move from chain to chain in the conduction process. The solution phase studies described here lie in a burgeoning context (only leading references are provided throughout this Account) of studies on molecular self-assembly. Pertinent examples are dye aggregates, 1 porphyrin and phthalocyanine aggregates and polymers, 2 columnar liquid crystals, 3 and donoracceptor complexes. 4 π-Stacks of ion radicals and mixed stacks of neutrals and ion radicals are well known in crystalline materials. 5 Indeed, much of the work described here can be considered an application of the concepts and methods developed for these crystalline electrical conductors. In general it is found that conductivity requires that the stacks be mixed valence, ie, partially oxidized or reduced. This can be achieved by crystallization of mixed valence salts, eg,(TTF) 3 (BF4) 2, or charge transfer salts in which there are segregated stacks of the partially oxidized and the partially reduced compounds, eg, TTF and TCNQ. 5