The extension of materials science to two dimensions is an extremely active and successful field of research. The treatment of the enormous amount of information already available on 2D materials can be best characterized by the fundamental chemical principles governing the periodic table. The 'aufbau' principle not only helps to understand the related features of monolayers that allows to catagorize the impressive results, it also induced the prediction of new stable 2D structures as already demonstrated in several cases. Since monolayers and few-layer assemblies appear as insulators, semiconductors, and metals, it is possible to construct nanoscale devices. The summary highlights the enormous progress made in realizing physical properties such as topological, superconducting, ferroelectric, piezoelectric, thermoelectric, and magnetic properties in 2D materials by presenting state-of-the-art examples. In addition, the first successful steps in the construction of nanoscale devices in catalysis, photovoltaics, field-effect transisitors, batteries, and sensors are summerized. An outlook to future developments is presented, whenever appropriate.