Thrombospondins are large glycoproteins secreted by most cells and activated platelets which function in cell-cell and cell-matrix interactions. This chapter focuses on the role of thrombospondins in vascular development, vascular remodelling, and vascular disease. In particular, the function of thrombospondins in angiogenesis, atherogenesis and thrombosis will be discussed. It is beyond the scope of this chapter to discuss in any detail the gene structure and the role of thrombospondins in inflammation and wound repair, and in diseases such as cancer and malaria. These subjects have been comprehensively covered in other recent reviews (Lahav, 1993a, b; Bornstein and Sage, 1994; Hogg, 1994; Bornstein, 1995; Adams et al., 1995).