Physical processes that redistribute or remove angular momentum from protoplanetary disks can drive mass accretion onto the star and affect the outcome of planet formation. Despite ubiquitous evidence for accretion, the process(es) responsible remain a mystery. I will describe how measurements of disk sizes and IR spectroscopy of nearly edge-on disks may shed new light on this long-standing problem, in the latter case by directly probing disk accretion in action! The results may provide evidence for supersonic “surface accretion flows,” which have been found in MHD simulations of magnetized disks. The resulting inference, that disks are primarily quiescent at AU distances, is conducive to the formation and preservation of planets.