A modular approach is introduced which utilizes benzene as key building block for the construction of one-dimensional (1D) and three-dimensional (3D) polyphenylenes as well as for two-dimensional (2D) graphene sheets.The chemically controlled bottom-up approach toward graphenes has clear advantages over top-down methods in view of structural perfection and reproducibility.A particularly powerful case is the precision synthesis of graphene nanoribbons (GNRs) after immobilisation of precursors on surfaces with in-situ monitoring by scanning tunnelling microscopy (STM).It is the rigorous control over structure at different length scales which affords new functions in digital electronics and energy technology.