This article describes the most recent developments in the synthesis of three dimensional (3D) π-conjugated molecules and the elucidation of their properties accomplished by the authors’ group. Cycloparaphenylenes (CPPs) of different sizes and a cage-like 3D molecule were synthesized based on the platinum-mediated assembly of π-units and subsequent reductive elimination of platinum. The assembly of π-units mimics the self-assembly process for the formation of supramolecular transition metal-ligand complexes with 3D cages and polyhedral structures. Furthermore, reductive elimination of platinum successfully took place with high efficiency, despite the high strain energy of the target molecule. Several size-dependent properties of CPPs, namely the photophysical, redox, and host-guest chemistries, were also clarified. These results are of use for a molecular-level understanding of CNT physical properties as well as fullerene peapods. Theoretical and electrochemical studies suggest that small CPPs and their derivatives should be excellent lead compounds for molecular electronics.