The age of globular clusters

I review here recent developments which have affected our understanding of both the absolute age of globular clusters and the uncertainties in this ag e estimate, and comment on the implications for cosmological models. This p resent estimate is in agreement with the range long advocated by David Schr amm. The major uncertainty in determining ages of globular clusers based up on the absolute magnitude of the main sequence turn-off remains the uncerta inty in the distance to these clusters. Estimates of these distances have r ecently been upwardly revised due to Hipparcos parallax measurements, if on e calibrates luminosities of main sequence stars. However, it is important to realize that at the present time, different distance measures are in dis agreement. A recent estimate is that the oldest clusters are 11.5 +/- 1.3 G yr, implying a one-sided 95% confidence level lower limit of 9.5 Gyr, if st atistical parallax distance measures are not incorporated. Incorporating mo re recent measures, including Hipparcos-based statistical parallax measures , raises the mean predicted age to 12.8 +/- 1 Gyr, with a 95% confidence ra nge of 10-17 Gyr. I conclude by discussing possible improvements which may allow a more precise age distribution in the near future. (C) 2000 Elsevier Science B.V. All rights reserved.