The primary challenge for high-performance nanoparticle catalysts is the atomic-level control of active sites. This challenge has two aspects, highly defined synthesis and atomic-scale resolution charaterisation. In this talk the evolution of state-of-the-art synthesis of metal nanoparticle catalysis with atomic-level control will be discussed. A range of concepts will be discussed including how these nanoparticles can be decorated with a second metal to form single atom catalysts resilient to CO poisoning for methanol oxidation and platinum strings that are highly efficient hydrogen evolution catalysts (Figure 1). Developments in the transmission electron microscopy (TEM) atomic scale characterization of active sites will also be illustrated with the discussion of different imaging modes and how in situ TEM can be used to elucidate synthetic reaction mechanisms. Finally, there will be a perspective on the future of atom-level nanoparticle catalyst design through precise control of support structure and single atom location to further elevate electrocatalytic performance.