The self-assembly on surfaces is a potential driving force for the creation of bottom-up bidimensional (2D) nanostructures with features below the limit of typical lithographic top-down patterning techniques. Self-assembled molecular networks (SAMNs) exhibit appealing properties that can be tailored by properly tuning the features of the single molecules, as well as the interactions governing their self-assembly. For instance, SAMNs are typically stabilized by weak intermolecular forces such as van der Waals, hydrogen and halogen bonding. Furthermore, 2D polymerization of these systems could be a powerful method for the synthesis of robust organic nanostructures with conjugated bonds, which allow high charge-carrier mobility due to the presence of delocalized π-orbitals. In my research project I investigate SAMNs by means of scanning tunneling microscopy (STM), an extremely powerful characterization technique that allows to image features in the real space with sub-molecular resolution. In addition, density functional theory (DFT) calculations are also used for a better understanding of such systems. STM is a very versatile tool able to operate either in ultra-high vacuum (UHV) or in ambient condition. In the specific, the investigation of organic 2D structures at the solution/solid interface is motivated in prospect of possible low-cost fabrication methods on the large scale, as opposed to systems in UHV. A deep understanding of the formation of such organized molecular layers is an essential step towards the future incorporation of these molecular materials into devices.