  Cosmological gravitational particle production (CGPP) is the creation of
particles in an expanding universe due solely to their gravitational
interaction. These particles can play an important role in the cosmic history
through their connection to various cosmological relics including dark matter,
gravitational wave radiation, dark radiation, and the baryon asymmetry. This
review explains the phenomenon of CGPP as a consequence of quantum fields in a
time-dependent background, catalogs known results for the spectra and
cosmological abundance of gravitationally produced particles of various spins,
and explores the phenomenological consequences and observational signatures of
CGPP.
