With 2 plates and 5 figures in the text) A review of age determination techniques that have been applied to the family Canidae is presented. It is shown that the pattern of growth and development of the various species is very similar, the rate of development being greater in the smaller, shorter-lived species, and vice versa.The occurrence of annuli in the hard tissues of London foxes is demonstrated; these annuli can be used reliably for age determination, despite suggestions that temperate zone animals from weakly continental climates have indistinct annuli. The objective ages determined by cementum annuli are then used to investigate the value of less timeconsuming age determination techniques, particularly in the separation of the young-of-the-year from adults. The results obtained from different studies vary, and these diff'erences are discussed. It is suggested that the speed of development vanes slightly indifferent Red fox populations, and so caution must be exercised before data from one population areapplied to anotherpopulation.