The hair follicle has become an important model system to study developmental processes, stem cell regulation and tissue morphogenesis for several reasons. First, it provides an excellent system to explore developmental mechanisms used to modify the same basic toolbox of interactions to regulate different developmental processes and to obtain distinct developmental outcomes. For example, epithelial-mesenchymal interactions in the embryo set up the scene for hair follicle specification and formation, and subsequently those same interactions are redeployed to execute the hair cycle in the adult. Second, the hair follicle provides an accessible system to study stem cells and their interactions with the immediate environment, often called the niche. As hair follicles undergo cycles of growth, destruction, quiescence and regeneration, different stem cell populations with distinct properties are required to repetitively execute these cycles. For this, the niche must provide and construct a unique milieu to regulate stem cell activity. Third, the hair follicle allows the study of development from the perspectives of multiple biological processes. The transitions between the different phases of the hair cycle involve dramatic morphological alterations and therefore require the coordination of multiple biological processes such as proliferation, apoptosis, cell migration, cellular communication and signal transduction.