Dust, Gas, and Heavy Elements in the Interstellar Medium of Galaxies

Although it typically makes up only 1% (or less) of the mass of the interstellar medium (ISM) in a galaxy, interstellar dust is absolutely critical to how the ISM works. Dust is also the repository of a large fraction of the heavy elements, and thus is central to understanding the cosmic history of elemental enrichment in the universe.  The fraction of the available heavy elements locked in dust grains has often been treated as a constant, but there is clear evidence now from a variety of measurements that this is decidedly not the case.  I will describe efforts to measure the fraction of heavy elements that are in dust grains (aka the dust-to-metals ratio) and learn how it varies within and between galaxies. In the course of these efforts, I will describe new approaches to deal with long standing issues in how we trace dust, gas, and heavy elements in the ISM.