  I would like to review recent efforts of detailed chemical abundance
measurements for field Milky Way halo stars. Thanks to the advent of wide-field
spectroscopic surveys up to a several kpc from the Sun, large samples of field
halo stars with detailed chemical measurements are continuously expanding.
Combination of the chemical information and full six dimensional phase-space
information is now recognized as a powerful tool to identify cosmological
accretion events that have built a sizable fraction of the present-day stellar
halo. Future observational prospects with wide-field spectroscopic surveys and
theoretical prospects with supernova nucleosynthetic yields are also discussed.
