Planet formation via the accretion of mm to cm size particles, often called pebbles, has been recently invoked to explain the diversity of planetary types and systems, as well as our own Solar System. However, this formation mechanism heavily relies on the availability of pebbles in the outer disk (beyond tens of au) and the pebble inward flux. I will discuss recent ALMA observations constraining the amount of pebbles available in disks and their outermost location as a function of time. By combining infrared spectroscopy and the ALMA results, I will present tantalizing evidence for the inward drift of pebbles. Finally, I will speculate on how to constrain observationally the pebble inward flux and discuss cross-displinary collaborations that are necessary to make progress in this field.