  The complex spectral and timing properties of the high-energy emission from
the accretion flow in black-hole binaries, together with their strong
connection to the ejection of powerful relativistic jets from the system, can
be simplified and reduced to four basic states: hard, hard-intermediate,
soft-intermediate and soft. Unlike other classifications, these states are
based on the presence of sharp state transitions. I summarize this
classification and discuss the relation between these states and the physical
components contributing to the emitted flux.
