The self-assembling properties of a-conjugated oligo-, poly-, and cyclothiophenes (see Figure) have been studied with different techniques. Scanning tunneling microscopy on perfectly ordered two-dimensional monolayers at the solution-HOPG (highly oriented pyrolytic graphite) interface has successfully been applied. The submolecular resolution achieved in the STM images provides valuable lattice and molecular information. Supported by X-ray structure analyses of the 3D bulk material and by theoretical calculations, molecular conformations, molecule-molecule, and molecule-substrate interactions of the oligo-, poly-, and cyclomers hale been analyzed and discussed.