The message of the Kepler space mission is this: super-Earths abound in the universe. These are planets 1--4 Earth radii and 2--20 Earth masses, composed of solids and gas in proportions of 100:1 by mass. We describe how super-Earths/sub-Neptunes form within circumstellar disks of gas and dust. From basic astrophysical considerations of gas dynamical friction, gravitational scatterings and mergers, and atmospheric accretion by cooling, we infer a planet formation history that occurs largely in-situ, and late in the life of a protoplanetary disk. We show how the theory explains observed occurrence rate trends with stellar metallicity and orbital period, and can be expanded to accommodate rarer subpopulations such as sub-Saturns (a.k.a. ``super-puffs'') and Jupiters. Puzzles and prospects will be highlighted.