Since the initial description of thrombospondin in 1971, our knowledge of the protein has reached a point where some understanding of its physiologic and pathologic roles has accrued. Thrombospondin is a multifunctional glycoprotein whose demonstrated affinities for multiple ligands make it a versatile molecule that can participate in mediating or modulating cell adhesion, fibrin polymerization, fibrinolysis, and development. The recently defined primary structure will make an understanding of the functional aspects of this molecule more accessible, and the next several years promises to define the role of thrombospondin in human biology.