  We introduce the AGORA project, a comprehensive numerical study of
well-resolved galaxies within the LCDM cosmology. Cosmological hydrodynamic
simulations with force resolutions of ~100 proper pc or better will be run with
a variety of code platforms to follow the hierarchical growth, star formation
history, morphological transformation, and the cycle of baryons in and out of 8
galaxies with halo masses M_vir ~= 1e10, 1e11, 1e12, and 1e13 Msun at z=0 and
two different ("violent" and "quiescent") assembly histories. The numerical
techniques and implementations used in this project include the smoothed
particle hydrodynamics codes GADGET and GASOLINE, and the adaptive mesh
refinement codes ART, ENZO, and RAMSES. The codes will share common initial
conditions and common astrophysics packages including UV background,
metal-dependent radiative cooling, metal and energy yields of supernovae, and
stellar initial mass function. These are described in detail in the present
paper. Subgrid star formation and feedback prescriptions will be tuned to
provide a realistic interstellar and circumgalactic medium using a
non-cosmological disk galaxy simulation. Cosmological runs will be
systematically compared with each other using a common analysis toolkit, and
validated against observations to verify that the solutions are robust - i.e.,
that the astrophysical assumptions are responsible for any success, rather than
artifacts of particular implementations. The goals of the AGORA project are,
broadly speaking, to raise the realism and predictive power of galaxy
simulations and the understanding of the feedback processes that regulate
galaxy "metabolism." The proof-of-concept dark matter-only test of the
formation of a galactic halo with a z=0 mass of M_vir ~= 1.7e11 Msun by 9
different versions of the participating codes is also presented to validate the
infrastructure of the project.
