The center of the Galaxy is a prominent source in x-rays and gamma rays. The study of its high-energy (HE) emission is crucial to understanding the physical phenomena taking place in this dense and extreme environment, where the closest supermassive black hole (SMBH) to us, Sagittarius ${\mathrm{A}}^{\star }$, is lurking nearly invisible today in most of the energy spectrum. These phenomena are probably common to other galactic nuclei and may explain the feedback processes between nuclear regions and galaxies, which are so important for the overall evolution of the Universe. The Galactic Center HE emission is complex and consists of both thermal and nonthermal radiation produced by compact and extended sources, surrounded by more diffuse components. All these objects and media are interacting with each other in the narrow and dense Central Molecular Zone (CMZ). Some of them also show relevant extensions toward the Galactic poles, indicating energetic outflows that seem to link the center to the recently observed large Galactic polar structures. In spite of the fundamental advances obtained over the past 25 years with the most sensitive x-ray and gamma-ray observatories, several questions remain open to investigation. The main observational results and the open issues on the high-energy diagnostics of the Galactic nuclear activity are reviewed, with a focus on processes that take place in the CMZ, and, in particular, a discussion on the role of present and past SMBH activities in powering this region and possibly the entire Galaxy.

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• Cosmic ray sources
• Gamma ray astronomy
• X ray astronomy
• Astronomical black holes
• Galactic nuclei & quasars
• Interstellar medium
• Milky Way
• Neutron stars & pulsars