Abstract: Lepton scattering from the proton and nuclei provides snapshots of their structure. In the Standard Model, this structure is described by Quantum Chromodynamics in terms of quarks and gluons. A major goal of present and future nuclear physics is to understand quantitatively and comprehensively the structure of nuclei in terms of QCD. Ongoing, frontier studies using the CLAS12 spectrometer at Jefferson Lab will be described. New targets and ion sources of polarized He-3 are under development and will be discussed. Finally, the future Electron-Ion Collider will be introduced.