The Axion Dark Matter Experiment (ADMX) doesn't look like much. Yet the modest 4-meter-long metal cylinder, housed at the University of Washington's Center for Experimental Nuclear Physics and Astrophysics, is key to one of the more important and promising investigations in particle physics. Starting late next year, ADMX will search for elusive, superlight particles called axions, which might make up dark matter whose gravity holds the galaxies together. Axions are a dark horse for dark matter; most theorists prefer a different hypothesis, so-called weakly interacting massive particles, or WIMPs. But decades of searching have turned up no proof that WIMPs exist. Now ADMX researchers are about to put axions to the test. In the next few years, their data ought to provide a clear-cut yes-or-no answer about whether axions constitute the universe's dark matter.