  The abundance patterns of the most metal-poor stars in the Galactic halo and
small dwarf galaxies provide us with a wealth of information about the early
Universe. In particular, these old survivors allow us to study the nature of
the first stars and supernovae, the relevant nucleosynthesis processes
responsible for the formation and evolution of the elements, early star- and
galaxy formation processes, as well as the assembly process of the stellar halo
from dwarf galaxies a long time ago. This review presents the current state of
the field of "stellar archaeology" -- the diverse use of metal-poor stars to
explore the high-redshift Universe and its constituents. In particular, the
conditions for early star formation are discussed, how these ultimately led to
a chemical evolution, and what the role of the most iron-poor stars is for
learning about Population III supernovae yields. Rapid neutron-capture
signatures found in metal-poor stars can be used to obtain stellar ages, but
also to constrain this complex nucleosynthesis process with observational
measurements. Moreover, chemical abundances of extremely metal-poor stars in
different types of dwarf galaxies can be used to infer details on the formation
scenario of the halo. and the role of dwarf galaxies as Galactic building
blocks. I conclude with an outlook as to where this field may be heading within
the next decade. A table of ~1000 metal-poor stars and their abundances as
collected from the literature is provided in electronic format.
