Materials scientists today employ essentially the entire periodic table in creating modern technology. In an age of sharply increasing usage, it is reasonable to wonder about the supplies of these elemental building blocks. In this article, we review current and prospective supply and demand for a variety of metals. Although data are often sparse, available information suggests that current practices are likely to lead to scarcity for some metals in the not-too-distant future. We conclude by discussing policies that, if adopted, might defuse some of these concerns.