  VLBI at millimeter wavelengths (mm-VLBI) allows the detailed imaging of
compact galactic and extragalactic radio sources with micro-arcsecond scale
resolution, unaccessible by other observing techniques. Here we discuss the
scientific potential of mm-VLBI for present and future research on `Active
Galactic Nuclei' (AGN) and their powerful relativistic jets. With the new
generation of large radio telescopes and interferometer arrays operating in the
millimeter radio bands (e.g. ALMA), the ultimate vicinity of super massive
Black Holes, and eventually even their event horizon, could be imaged. With its
large collecting area, and in combination with these future telescopes, the
Sardinia Radio Telescope could form the World's `sharpest' astronomical imaging
machine.
