The ages of the oldest stars in the Milky Way yield a reliable lower limit to the age of the universe and provide important information on the early formation history of our Galaxy. I will provide an overview of the stellar age determination process, including a critical look at the uncertainties associated with determining the ages of stars. Evidence for a significant spread in ages among the old stars in the halo of the Milky Way will be presented and used to study the early formation history of our Galaxy. I will conclude by discussing the absolute age of the oldest stars and its implications for cosmology.