The role of von Willebrand factor (VWF) in blocking hemorrhage is centered on its ability to act as a bridging adhesive molecule between platelets and components of the extracellular matrix or other platelets. In the course of chronic vascular diseases, moreover, the same properties of VWF may become the cause of pathological thrombus formation leading to arterial occlusion. There is convincing evidence that VWF functions involving interactions with platelets ultimately depend on binding to the membrane glycoprotein (GP) Ibalpha receptor mediated by the A1 domain. In this review, we present the current knowledge on the structural features of the VWF A1 domain that support its functions.