Invited review abstract

Explosive phenomena of magnetic energy conversion in the solar corona lead to the production of energetic particles at all energies. These particles play a major role in the active Sun since they contain a large amount of the energy released during flares. I shall review here the available information on solar particle acceleration provided by X-ray and gamma-ray observations, with peculiar emphasis on the results obtained recently by the RHESSI mission. Radio observations from mm to cm wavelengths provide complementary diagnostics on the spectra and number of energetic electrons.I shall also discuss the observations of flares in the recently opened window in the 200-400 GHz range. All the observational results will be discussed in the context of particle acceleration and transport models in the solar atmosphere.