  We present a new scenario for the behaviour of Be/X-ray binaries based on
long-term multiwavelength monitoring and the decretion disc model. The
circumstellar discs of the primaries are truncated because of the tidal and
resonant effect of the neutron star. The geometry of the systems and the value
of viscosity determine the presence or absence of Type I X-ray outbursts. The
interaction of a strongly disturbed disc with the neutron star originates Type
II X-ray and optical outbursts.
