(Uploaded by Plazi for the Bat Literature Project) As bats are long-lived mammals, insight into the age of individuals is important for studies relating to population ecology and conservation biology, as well as longevity. Thus, there is a need to develop methods to estimate the age of bats, and teeth are excellent means to do so. The work detailed here involves an assessment of age-related changes and variation in tooth wear, dentine growth layers, and pulp cavity size in two bat species with differing life history strategies, i.e. Nyctalus noctula (n = 149) and Eptesicus serotinus (n = 49). Both the gross morphology and the histology of teeth in both species were found to display age-related variation. Morphological indicators like tooth wear and pulp-cavity size showed considerable variation at the individual level, and corresponding with broadly defined age categories. Dentine growth layering was consistent with presumed age and had annual growth layers in both species, along with accessory layers. Aspects of interpreting growth layers and tooth wear based on photographs and histological preparations associated with observer bias are important to consider, as are the sampling of multiple readings.