The last ten years have seen dramatic developments in our understanding of the surface science of nanoparticles grown on solid surfaces. These developments are continuing apace, not least in our understanding of nanoparticle structures at the atomic scale. Well-defined materials can now be prepared and the detailed nature of reactions at the atomic and molecular scale are emerging. Ensemble-averaging techniques are being combined with local, atomically-resolving probes such as STM, exposing such materials to scientific understanding, especially regarding local morphology and its effect on reactivity and catalysis. Current developments include in-situ measurements of catalytic reactivity at high pressure and temperature. We look forward to welcoming you to Berlin for this Faraday Discussion