  I briefly review the theory of soft X-ray transient systems. Irradiation of
the accretion disc faces by the central X-ray source determines both the
occurrence and the nature of the outbursts, in particular forcing these to be
long viscous events and producing exponential decays at short orbital periods.
Soft X-ray transients constitute the majority of LMXBs, persistent systems
being largely confined to a subset of neutron-star LMXBs with periods P < 2 d.
It appears that LMXBs very frequently contain nuclear-evolved companions, even
at short orbital periods. In long-period transients (P > 20 d) the outburst
recurrence times must become extremely long (> 1500 yr). The outbursts are
highly super-Eddington, markedly reducing the accretion efficiency. Spinup of a
neutron-star primary to millisecond periods probably cannot occur for orbital
periods > 200 d, in agreement with observations of binary pulsars.
