A recent international collaboration between the UK, France, US and Canada have performed systematic studies of both nuclear radii and binding energies in (even) oxygen isotopes from the valley of stability to the neutron drip line. Both charge and matter radii are compared to state-of-the-art ab initio calculations along with binding energy systematics. Experimental matter radii are obtained through a complete evaluation of the available elastic proton scattering data of oxygen isotopes. The theoretical ab initio calculations were possible thanks to exploiting High Performance Computing resources and showed that, in spite of a good reproduction of binding energies, conventional nuclear interactions derived within chiral effective field theory fail to provide a realistic description of charge and matter radii. A novel version of two- and three-nucleon forces leads to considerable improvement of the simultaneous description of the three observables for stable isotopes but shows deficiencies for the most neutron-rich systems. Thus, crucial challenges related to the development of nuclear interactions remain. Phys. Rev. Lett. 117, 052501 (2016) – Editor’s suggestion.