Transforming growth factor β (TGFβ) pathways are implicated in metazoan development, adult homeostasis and disease. TGFβ ligands signal via receptor serine/threonine kinases that phosphorylate, and activate,intracellular Smad effectors as well as other signaling proteins. Oligomeric Smad complexes associate with chromatin and regulate transcription, defining the biological response of a cell to TGFβ family members. Signaling is modulated by negative-feedback regulation via inhibitory Smads. We review here the mechanisms of TGFβ signal transduction in metazoans and emphasize events crucial for embryonic development.