The transforming growth factor b (TGF-b) family of signaling molecules, which includes TGF-bs, activins, inhibins, and numerous bone morphogenetic proteins (BMPs) and growth and differentiation factors (GDFs), has important functions in all cells and tissues, including soft connective tissues and the skeleton. Specific TGF-b family members play different roles in these tissues, and their activities are often balanced with those of other TGF-b family members and by interactions with other signaling pathways. Perturbations in TGF-b family pathways are associated with numerous human diseases with prominent involvement of the skeletal and cardiovascular systems. This review focuses on the role of this family of signaling molecules in the pathologies of connective tissues that manifest in rare genetic syndromes (e.g., syndromic presentations of thoracic aortic aneurysm), as well as in more common disorders (e.g., osteoarthritis and osteoporosis). Many of these diseases are caused by or result in pathological alterations of the complex relationship between the TGF-b family of signaling mediators and the extracellular matrix in connective tissues.T he transforming growth factor b (TGF-b) family of cytokines comprises the three TGF-b proteins (TGF-b1, TGF-b2, and TGFb3) and related growth and differentiation factors such as activins, inhibins, bone morphogenic proteins (BMPs), and growth and differentiation factors (GDFs). These molecules play critical roles both in normal development and in several pathological conditions, including inflammation, fibrosis, and cancer (reviewed in Li and Flavell 2006;Gordon and Blobe 2008;Ikushima and Miyazono 2010). This review focuses on the role of these proteins in development and homeostasis of the skeleton and other connective tissues (summarized in Fig. 1) and on the diseases that ensue when these pathways are altered. Aberrant signaling in these pathways has been associated with common connective 6 These authors contributed equally to this work.