Nuclear structure and reactions can be linked to the underlying theory of Quantum Chromodynamics (QCD) through an effective field theory (EFT) of nucleons, Pionless EFT. Involving only nucleons, this EFT is the low-energy limit of QCD appropriate for the ground states of light nuclei both both physical quark masses and the larger masses accessible to Lattice QCD simulations. I will describe recent efforts to apply this EFT to medium-mass nuclei such as 16O.