Rare-earths combine particularly easily with other elements to form useful compounds and alloys, such as neodymium-iron-boron, the strongest, lightest magnet for motors. "No other element can do that," says Jack Lifton, an independent metals consultant. "Once we've used them up, the periodic table is closed for business." Similar stories are playing out across the table. For many elements, we'll eventually need to find more, recycle, or move on to another. Launch the gallery for a status report for 10 of them.