  Solar filament eruptions play a crucial role in triggering coronal mass
ejections (CMEs). More than 80 % of eruptions lead to a CME. This correlation
has been studied extensively during the past solar cycles and the last long
solar minimum. The statistics made on events occurring during the rising phase
of the new solar cycle 24 is in agreement with this finding. Both filaments and
CMEs have been related to twisted magnetic fields. Therefore, nearly all the
MHD CME models include a twisted flux tube, called a flux rope. Either the flux
rope is present long before the eruption, or it is built up by reconnection of
a sheared arcade from the beginning of the eruption. In order to initiate
eruptions, different mechanisms have been proposed: new emergence of flux,
and/or dispersion of the external magnetic field, and/or reconnection of field
lines below or above the flux rope. These mechanisms reduce the downward
magnetic tension and favor the rise of the flux rope. Another mechanism is the
kink instability when the configuration is twisted too much. In this paper we
open a forum of discussions revisiting observational and theoretical papers to
understand which mechanisms trigger the eruption. We conclude that all the
above quoted mechanisms could bring the flux rope to an unstable state.
However, the most efficient mechanism for CMEs is the loss-of-equilibrium or
torus instability, when the flux rope has reached an unstable threshold
determined by a decay index of the external magnetic field.
