I study the astrophysical properties of dark matter, thus far via optical imaging, spectroscopy and dynamical modeling of the 'dwarf' galaxies that surround the Milky Way and neighboring Andromeda. The dwarf galaxies include the oldest, smallest and 'darkest' (i.e., composed almost entirely of dark matter) galaxies known, and currently represent the smallest physical scales (sizes of ≈ 100 light years, speeds of a few kilometers per second, masses of ≈ 100,000 Suns) that are associated empirically with dark matter. If dark matter is made from some kind of new fundamental particle, then the manner in which dark matter can form 'clumps' at such small scales can help to decide among various ideas about the properties of that particle. By measuring the spatial distribution of dark matter in dwarf galaxies, I aim to help figure out what the dark matter actually is. Thus my research has wandered into the intersection of dynamics, cosmology and particle physics.