White dwarfs represent the endpoint of the evolution of the large majority of stars formed in the Galaxy. 
Their usefulness as cosmochronometers has been recognized since about 50 years ago, but only in the last 
two decades observations and theory have improved to a level that has made possible to employ white dwarfs 
for determining ages of the stellar populations in the nearest star clusters. 
This talk will be centred on the theory behind the methods for white dwarf age-dating,
the related uncertainties, and their application to open and globular clusters.