Sarah Millar of the University of Pennsylvania summarizes our current state of knowledge of the molecular events that control hair follicle, mammary gland and sweat gland development. She also highlights major questions still remaining. Using the mammary gland as an example, she discusses how evolutionary pressures may have driven specific changes in molecular pathways to permit organ diversification, and further refinements in glandular number and location that permitted efficient feeding of newborn mammals including humans. (#30215)