Solar flares - the most powerful explosions in the solar system - essentially convert the intrinsic energy of the coronal magnetic field into the kinetic energy of accelerated particles. The process of magnetic reconnection is widely discussed as a mechanism for doing this, but the detailed physics of particle acceleration has thus far remained elusive. The most direct diagnostics of flare-accelerated particles are provided by hard X-ray and gamma-ray observations. After an extensive introduction, I will review recent hard X-ray and Gamma-ray observations obtained by the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI), a NASA small explorer mission. Furthermore, I will briefly describe desired future instrumentation including a sounding rocket experiment called FOXSI that will test hard X-ray focusing optics for solar observations.