Millimeter-Wavelength Very Long Baseline Interferometry is interferometry at millimeter wavelengths (3.5-1.3mm: 86GHz-230GHz) with disconnected telescopes using the longest baselines on Earth (1000-10000km) in order to achieve the highest angular resolution (0.01 - 0.00005). The disconnected telescopes need special time/frequency references provided by the observatory-own Hydrogen-masers, synchronized to GPS time signals. The observations are recorded on tape for correlation at special correlator stations. The correlation gives visibility tables. mm-VLBI sees only sources which emit non-thermal radiation at brightness temperatures of T 10-10K. These sources represent the 'hot' and energetic component of the Universe, for instance masers and quasars.