As physicists developed plans for building an electron-ion collider (EIC)—a next-generation nuclear physics facility to be built at the U.S. Department of Energy's Brookhaven National Laboratory for nuclear physics research—they explored various options for accelerating the beams of electrons. One approach, developed by scientists at Brookhaven Lab and Stony Brook University, was to use an energy-recovery linear accelerator (ERL). The ERL would bring the electrons up to the energy needed to probe the inner structure of protons and atomic nuclei, and then decelerate the electrons and reuse most of their energy. The R&D to develop the innovative ERL may end up having a major impact in a different area of physics—high-energy particle physics, where the power needs make its energy-saving features particularly attractive.