  High energy gamma-ray astronomy is a newly emerging and very successful
branch of astronomy and astrophysics. Exciting results have been obtained by
the current generation Cherenkov telescope systems such as H.E.S.S., MAGIC,
VERITAS and CANGAROO. The H.E.S.S. survey of the galactic plane has revealed a
large number of sources and addresses issues such as the question about the
origin of cosmic rays. The detection of very high energy emission from
extragalactic sources at large distances has provided insights in the star
formation during the history of the universe and in the understanding of active
galactic nuclei. The development of the very large Cherenkov telescope array
system (CTA) with a sensitivity about an order of magnitude better than current
instruments and significantly improved sensitivity is under intense discussion.
This observatory will reveal an order of magnitude more sources and due to its
higher sensitivity and angular resolution it will be able to detect new classes
of objects and phenomena that have not been visible until now. A combination of
different telescope types will provide the sensitivity needed in different
energy ranges.
