Gamma-rays represent the most energetic photons of the electromagnetic spectrum. Astronomy with gamma-rays, therefore, allows the study of the most compact, energetic and violent objects in the Universe: neutron stars, stellar and supermassive black holes, supernovae including their remnants and cosmic rays interacting in the interstellar medium. An overview is given of the history of gamma-ray astronomy, the production mechanisms for gamma-rays and of the main results achieved.