  Relativistic outflows are common in accreting and forming black holes.
Despite the enormous differences in scale, stellar-mass black holes in X-ray
binaries and supermassive black holes in Galactic Nuclei produce jets with
analogous properties. In both are observed two types of relativistic outflows:
1) quasi-steady compact jets with flat-spectrum, and 2) episodic large-scale
ejections with steep-spectrum and apparent superluminal motions. Because of the
short time scale of the phenomena in black hole binaries, the formation of
synchrotron jets is associated to changes in the X-ray thermal emission from
the accretion disk. Besides, the most common class of gamma-ray bursts can be
conceived as extreme microquasars, since they are afterglows from
ultra-relativistic jets associated to the formation of black holes at
cosmological distances.
