  We review the current status of axion cosmology in the light of recent work.
We conclude that in the standard scenario, in which a global string network
forms at the Peccei-Quinn phase transition, the largest contribution to the
axion density is from loops, even when uncertainties in the nature of the QCD
phase transition are taken into account. We also briefly discuss the
implications of non-standard scenarios, such as an inflationary epoch and
entropy production.
