The development of skin appendages such as hairs, teeth, and mammary glands is regulated by signaling molecules of the Wnt, FGF, TGFbeta, and Hedgehog pathways. Last decade has also revealed a pivotal role for the TNF family ligand ectodysplasin (Eda) in multiple steps of epithelial appendage morphogenesis, from initiation to differentiation. Surprisingly, other members of the TNF superfamily such as Rank ligand, lymphotoxins, and TNF have recently been linked with specific aspects of skin appendage biology including branching of the mammary gland, hair shaft formation, and hair follicle cycling. This review focuses on the novel discoveries of Eda and other TNF related cytokines in skin appendage development made since the previous review on this topic in Cytokine and Growth Factor reviews in 2003.