  Solar flares are accessible to a broad variety of observational methods to
see and investigate the {\em magnetic reconnection} phenomenon in
high-temperature strongly-magnetized plasma of the solar corona. An analysis of
the topological peculiarities of magnetic field in active regions shows that
the {\em topological trigger} effect is necessary to allow for in order to
construct models for large eruptive flares. The topological trigger is not a
resistive instability which leads to a change of the topology of the field
configuration from pre- to post reconnection state. On the contrary, the
topological trigger is a quick change of the global topology, which dictates
the fast reconnection of collisional or collisionless nature. The current state
of the art and development potential of the theory of collisionless
reconnection in the strong magnetic fields related to large flares are briefly
reviewed. Particle acceleration is considered in collapsing magnetic traps
created by reconnection. In order to explain the formation of coronal X-ray
sources, the Fermi acceleration and betatron mechanism are simultaneously taken
into account analytically in a collisionless approximation. Finally, the
emphasis is on urgent unsolved problems of solar flare physics.
