The Electron-Ion Collider (EIC), designed by a partnership between Brookhaven National Laboratory (BNL) and Thomas Jefferson National Accelerator Facility (TJNAF), will seek to answer how nucleons — neutrons and protons — are assembled to form the nuclei of atoms, and uniquely address three profound questions about them: • How does the mass of the nucleon arise?• How does the spin of the nucleon arise?• What are the emergent properties of dense systems of gluons? The mission need for the new collider was acknowledged by the U.S. Department of Energy, and CD-0 was granted on December 19, 2019.