The ordering of small molecules, programmed with functional groups for specific non-covalent interactions, can lead to robust, dynamic, and functional monolayers or thin films. Our group studies these assemblies under well-controlled environments by atomic-resolution scanning tunneling microscopy (structural characterization) and X-ray photoelectron spectroscopy (chemical characterization). These studies allow new insights in the roles of ionic bonding, donor-acceptor stacking, transition metal coordination, dipole interactions, and van der Waals interactions in two-dimensional assembly, as well as in the formation of crystalline organic thin films. In this presentation, new discoveries from our lab will be shown that push the frontiers of molecular self-assembly, including highly robust 2D architectures (stable to 180 C), chemical stability by interfacial layer design, surprisingly crystalline multilayers through surface templating and donor-acceptor stacking, and chemically-triggered switching of dynamic supramolecular structures (at the liquid-solid interface). These studies open new opportunities in designing organic materials for organic electronics, sensors, catalysts and photovoltaics.