Nearly a decade has passed since the discovery that planets with sizes intermediate between that of the Earth and Neptune ("super-Earths" or "mini-Neptunes", depending on their densities) dominate the observed population of close-in exoplanets. These planets have no solar system analogue, yet 30% of Sun-like stars appear to have at least one (and often more) interior to Mercury's orbit. Did these planets form in situ, or did they migrate inward from a more distant formation location? Either way, the implications for our understanding of planet formation are bound to be significant. In my talk I will describe current efforts to address this question by characterizing the bulk densities and compositions of these planets and searching for outer gas giant companions.