The Key Science Projects of the Cherenkov Telescope Array

The Cherenkov Telescope Array (CTA) will be the next generation gamma-ray observatory, open to the scientific community, to investigate the very high-energy emission from a large variety of celestial sources in the energy range 20 GeV -300 TeV. The full array, distributed over two sites, one in the northern and one in the southern hemisphere, will provide whole-sky coverage and will improve by about one order of magnitude the sensitivity with respect to the current major arrays. CTA will investigate a much higher number of already known classes of sources, going to much larger distances in the Universe, performing population studies, accurate variability and spatially-resolved studies. Moreover, new light will be shed on possible new classes of high-energy sources, such as GRBs, cluster of Galaxies, Galactic binaries, and on fundamental physics. By pushing the high-energy limit to E> 100 TeV it will allow a thorough exploration of the cut-off regime of the cosmic accelerators. We review the main CTA Key Science Projects, which will focus on major scientific cases, a clear advance beyond the current state of the art, and we discuss the production of legacy data-sets of high value to a wider community.