  The last two decades have seen a great improvement in our understand- ing of
the complex phenomenology observed in transient black-hole binary systems,
especially thanks to the activity of the Rossi X-Ray Timing Explorer satellite,
com- plemented by observations from many other X-ray observatories and
ground-based radio, optical and infrared facilities. Accretion alone cannot
describe accurately the intricate behavior associated with black-hole
transients and it is now clear that the role played by different kinds of
(often massive) outflows seen at different phases of the outburst evolution of
these systems is as fundamental as the one played by the accretion process
itself. The spectral-timing states originally identified in the X-rays and
fundamentally based on the observed effect of accretion, have acquired new
importance as they now allow to describe within a coherent picture the
phenomenology observed at other wave- length, where the effects of ejection
processes are most evident. With a particular focus on the phenomenology seen
in the X-ray band, we review the current state-of-the-art of our knowledge of
black hole transients, describing the accretion-ejection connection at play
during outbursts through the evolution of the observed spectral-timing
properties. Although we mainly concentrate on the ob- servational aspects of
the global X-ray transient picture, we also provide physical insight to it by
reviewing (when available) the theoretical explanations and models proposed to
explain the observed phenomenology.
