  Nucleocosmochronology involves the use of the abundances of radioactive
nuclear species and their radiogenic decay daughters to establish the finite
age of the elements and the time scale for their formation. While there exist
radioactive products of several specific nucleosynthesis mechanisms that can
reveal the histories of these mechanisms, it is the long lived actinide
isotopes {232}Th, {235}U, and {238}U, formed in the r-process, that currently
play the major role in setting the time scale of Galactic nucleosynthesis. Age
determinations in the context of Galactic chemical evolution studies are
constrained by intrinsic model uncertainties. Recent studies have rather taken
the alternative approach of dating individual stars. Thorium/europium dating of
field halo stars and globular cluster stars yields ages on the order of 15 +/-
4 Gyr. A solid lower limit on stellar ages is available as well, for stars for
which one both knows the thorium abundance and has an upper limit on the
uranium abundance. For the cases of the two extremely metal deficient field
halo stars CS 22892-052 and HD 115444, lower limits on the nuclear age of
Galactic matter lie in the range 10-11 Gyr. Th/U dating of the star CS 31082-00
gives an age of 12.5 +/- 3 Gyr. Observations of thorium and uranium abundances
in globular cluster stars should make possible nuclear determinations of the
ages of clusters that can be compared with ages from conventional stellar
evolution considerations.
