Celestial gamma rays are absorbed in the atmosphere. However at high energies, above a few tens of GeV, they may be detected on ground, though indirectly, through their interactions in the atmosphere. I shall introduce the subject of ground-based gamma-ray astronomy using the atmospheric Cherenkov technique and briefly trace its historical development in India. The current facilities at Hanle (Ladakh) will be highlighted along with other operating ground-based facilities elsewhere for gamma ray astronomy. After discussing some of the sources of gamma rays, I will conclude with the future prospects, especially with the Cherenkov Telescope Array (CTA), an international project for the next generation of observatories in this field covering a broad energy range from 20 GeV to 300 TeV.