  A jet model for Galactic black-hole X-ray binaries will be presented that
appears to explain several observational characteristics. In particular, it
explains the energy spectrum from radio to hard X-rays, the time-lags as a
function of Fourier frequency, the increase of the variability amplitude (QPO
and high frequency) with increasing photon energy, and the narrowing of the
autocorrelation function with increasing photon energy. On the other hand,
there are additional observational constraints that no model has tried to
explain yet. It is important that we all try to address these constraints if we
are to make any progress in understanding black-hole X-ray sources
