There is an accumulating body of observational evidence which seems to
support the view that the duration of the phase of star formation and
nucleosynthesis activity in the halo of our Galaxy may have been of t
he order of 2-3 x 10(9) years. Such evidence arises from abundance det
erminations for metal-deficient field halo stars and globular cluster
stars, as well as from age determinations for the local white dwarf po
pulation and for the halo and disk populations of globular clusters. W
e briefly review these diverse observational constraints on the timesc
ale of halo evolution and discuss some possible implications for dynam
ical models for the collapse of the halo and the onset of star formati
on activity in the Galactic disk.