I review some of the basic observational details of jets from X-ray binaries, or ‘micro-quasars.’ It is shown that in both (Z and Atoll) NS and BHC systems radio emission, and therefore jet formation, is correlated with the presence of hard (30–500 keV) X-ray emission. At &ggr;-ray (>500 keV) energies, the relation is not so clear. Possible physical connections between the presence of a jet, with a population of relativistic electrons, and the emission of hard X-rays, are briefly discussed. ©2001 American Institute of Physics.