  The preliminary design of the new space gamma-ray telescope GAMMA-400 for the
energy range 100 MeV - 3 TeV is presented. The angular resolution of the
instrument, 1-2{\deg} at E{\gamma} ~100 MeV and ~0.01^{\circ} at E{\gamma} >
100 GeV, its energy resolution ~1% at E{\gamma} > 100 GeV, and the proton
rejection factor ~10E6 are optimized to address a broad range of science
topics, such as search for signatures of dark matter, studies of Galactic and
extragalactic gamma-ray sources, Galactic and extragalactic diffuse emission,
gamma-ray bursts, as well as high-precision measurements of spectra of
cosmic-ray electrons, positrons, and nuclei.
