  Observational aspects of solar flares relevant to the acceleration process of
electrons and protons are reviewed and it is shown that most of these
observations can be explained by the interaction with flare plasma of a power
law energy distribution of electrons (and protons) that are injected at the top
of a flaring loop, in the so-called thick target model. Some new observations
that do not agree with this model are described and it is shown that these can
be explained most naturally if most of the energy released by the reconnection
process goes first into the generation of plasma turbulence, which accelerates,
scatters and traps the ambient electrons near the top of the loop
stochastically. The resultant bremsstrahlung photon spectral and spatial
distributions agree with the new observations. This model is also justified by
some theoretical arguments. Results from numerical evaluation of the spectra of
the accelerated electrons and their bremsstrahlung emission are compared with
observations and shown how one can constrain the model parameters describing
the flare plasma and the spectrum and the energy density of the turbulence.
