The NASA Kepler Mission demonstrated that planets larger than Earth yet smaller than Neptune are a commonplace in the galaxy. Until recently, we knew nothing about their masses and, by inference, their compositions.  I report on what we've learned from the first 3 years of the HARPS-N survey, which aims to understand the transition from rocky planets, composed of rock and iron, to Neptune-like worlds, which have accreted an envelope of primordial H/He gas. I will explain the role of the NASA Transiting Exoplanet Survey Satellite (TESS), scheduled for launch in 2017.