  This review focuses on the processes that energize and trigger major solar
flares and flux-rope destabilizations. Numerical modeling of specific solar
regions is hampered by uncertain coronal-field reconstructions and by poorly
understood magnetic re- connection; these limitations result in uncertain
estimates of field topology, energy, and helicity. The primary advances in
understanding field destabilizations therefore come from the combination of
generic numerical experiments with interpretation of sets of observations.
These suggest a critical role for the emergence of twisted flux ropes into
pre-existing strong field for many, if not all, of the active regions that pro-
duce M- or X-class flares. The flux and internal twist of the emerging ropes
appear to play as important a role in determining whether an eruption will
develop predom- inantly as flare, confined eruption, or CME, as do the
properties of the embedding field. Based on reviewed literature, I outline a
scenario for major flares and erup- tions that combines flux-rope emergence,
mass draining, near-surface reconnection, and the interaction with the
surrounding field. Whether deterministic forecasting is in principle possible
remains to be seen: to date no reliable such forecasts can be made.
Large-sample studies based on long-duration, comprehensive observations of
active regions from their emergence through their flaring phase are needed to
help us better understand these complex phenomena.
