The rapid advances in the exoplanet field have culminated with the discovery of a new class of planets. These sub-Neptune and super-Earth-size exoplanets have proven to be ubiquitous in our Galaxy, yet our own Solar System is completely void of such planets. Moreover, the composition of these planets is almost entirely unknown. To understand the nature of this emerging planetary regime where the majority of exoplanets reside, we must evolve from mere discovery to a detailed characterization of these worlds. Characterizing these planets will lead to an improved understanding of the most abundant type of planets in our Galaxy, allowing us to place our Earth and our Solar System in a galactic context, improve our understanding of how the planets formed and facilitate our understanding of where life outside our Solar System could potentially evolve.