Adult mammalian epidermis is maintained by proliferation of stem cells and differentiation of their progeny. In undamaged epidermis stem cells in a particular location only give rise to the lineages that are appropriate for that location. However, following wounding or genetic manipulation any epidermal stem cell is capable of repopulating all of the epidermal lineages, revealing a remarkable degree of plasticity. My lab is currently using a range of in vitro and in vivo approaches to define the environmental signals that regulate epidermal stem cell fate. Our studies highlight the importance of the Wnt and Notch pathways and reveal the role of reciprocal interactions between epidermal cells and cells of the dermis. Furthermore, they show that stem cells in different locations respond differently to the same signal, raising the question of the extent to which stem cell behaviour is hard-wired or environmentally regulated.