The transforming growth factor β (TGFβ) pathway occupies a central position in the signaling networks that control the growth, differentiation, and final fate of metazoan cells. Over the past few years, remarkable progress has been made in identifying the central components of this pathway, defining their interactions, and deciphering how a cell interprets its signals. Along the way, genetic alterations have been discovered in this pathway that provide answers to long-standing questions about the molecular basis of certain common somatic disorders as well as rare inherited ones. Recent reviews have covered TGFβ signal transduction (