  Black hole X-ray binaries are transient probably because their discs are
subject to the same thermal-viscous instability which is present in dwarf nova
binary systems. I discuss applications of the dwarf-nova instability model to
transient, low-mass, X-ray binary systems. When disc truncation and X-ray
irradiation are taken into account this model is capable of reproducing the
basic properties of X-ray binary outbursts (Dubus et al. 2000).
