The Electron-Ion Collider (EIC), planned to be built at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory (BNL), in partnership with Thomas Jefferson National Accelerator Facility (Jefferson Lab), will be the most advanced tool for studying some of the deepest unexplored recesses of the atom. It will peer into protons and neutrons, the building blocks that make up atomic nuclei, providing unprecedented insight into how those particles' internal building blocks—and the gluelike force that holds them together—build up the structure of nearly all visible matter in the Universe.