Why Do Black--Hole X-ray Binaries Tend to Be Transient?

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).