2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/5264Until recently, VLBI targets have been drawn almost exclusively from the brightest and most compact radio sources in the sky, with typical flux densities well in excess of a few tens of mJy. These sources are predominantly identified with Active Galactic Nuclei (AGN), located at cosmological distances. In this lecture I will attempt to summarise what is currently known about the general properties of the faint sub-mJy and microJy radio source population, as determined from deep multi-wavelength studies of the HDF-N. In particular, I will try to provide a VLBI perspective, describing the first deep, wide-field, VLBI pilot observations of the HDF, together with a summary of the main results. The role VLBI can play in future high resolution studies of faint radio sources is also addressed.11 pages, 8 figures. To appear in "The Role of VLBI in Astrophysics, Astrometry and Geodesy", NATO ASI VLBI 2001 School, editor: F. MantovaniAstrophysicstext