  Hard X-rays and gamma-rays are the most direct signatures of energetic
electrons and ions in the sun's atmosphere which is optically thin at these
energies and their radiation involves no coherent processes. Being collisional
they are complementary to gyro-radiation in probing atmospheric density as
opposed to magnetic field and the electrons are primarily 10--100 keV in
energy, complementing the (>100 keV) electrons likely responsible for microwave
bursts.
  The pioneering results of the Ramaty High Energy Solar Spectroscopic Imager
(RHESSI) are raising the first new major questions concerning solar energetic
particles in many years. Some highlights of these results are discussed --
primarily around RHESSI topics on which the authors have had direct research
involvement -- particularly when they are raising the need for re-thinking of
entrenched ideas. Results and issues are broadly divided into discoveries in
the spatial, temporal and spectral domains, with the main emphasis on flare
hard X-rays/fast electrons but touching also on gamma-rays/ions, non-flare
emissions, and the relationship to radio bursts.
