  I present an introductory review text, focusing on recent deep field studies
using radio telescopes, including high-resolution, wide-field VLBI
observations. The nature of the faint radio source population is discussed,
taking into account complimentary data and results that are now available via
the sub-mm, IR, optical and X-ray wave-bands. New developments regarding the
increased sensitivity of VLBI and an expansion in the instruments field-of-view
are also presented. VLBI may be an important tool in recognising distant,
obscured AGN from the ``contaminant'' star forming galaxies that now dominate
lower-resolution, sub-arcsecond and arcsecond radio observations.
