AbstractHypohidrotic (anhidrotic) ectodermal dysplasia (HED) is a congenital syndrome characterized by sparse hair, oligodontia, and reduced sweating. It is caused by mutations in any of the three Eda pathway genes: ectodysplasin (Eda), Edar, and Edaradd which encode a ligand, a receptor, and an intracellular signal mediator of a single linear pathway, respectively. In rare cases, HED is associated with immune deficiency caused by mutations in further downstream components of the Eda pathway that are necessary for the activation of the transcription factor NF‐κB. Here I present a brief research update on the molecular aspects of this evolutionarily conserved pathway. The developmental role of Eda will be discussed in light of loss‐ and gain‐of‐function mouse models with emphasis on the past few years. © 2009 Wiley‐Liss, Inc.