Basic objective of this lecture is to present on Gamma Rays. Gamma rays have the smallest wavelengths and the most energy of any other wave in the electromagnetic spectrum. These waves are generated by radioactive atoms and in nuclear explosions. It is the most potent particles on the electromagnetic scale and the known universe. They only created by radioactive atoms and nuclear reactions. Here also focus on the finding of a new class of objects–high energy gamma-ray emitting blazars, or grazars.