Transforming growth factor beta (TGFβ) is the prototype for a large, and still growing, family of growth factors related by their invariant positioning of seven cysteine residues which contribute to a unique structural feature called the 'cysteine knot". Of the proteins belonging to the TGFβ family, the TGFβ themselves are possibly the most pleiotropic and multifunctional, affecting processes ranging from regulation of cellular differentiation and growth to inflammation, wound healing, and bone formation, and contributing to the pathogenesis of diseases as diverse as autoimmune disease and carcinogenesis. Consistent with the multiple tissues and diseases in which TGFβ has been demonstrated to play a role, the cellular targets are not restricted to any lineages or cell types. Any cell can express TGFβ receptors and secrete TGFβ ligand. In this review we highlight some of the aspects of TGFβ structure and function with emphasis on its cellular activities, its regulation, and its roles in disease pathogenesis.