Platelet membranes are rich in glycoproteins which mediate the key functions of platelets, adhesion and aggregation, by their binding of specific adhesive proteins. The membrane glycoproteins were initially identified by surface labeling with 125I or 3H followed by SDS-polyacrylamide gel electrophoresis. Many of these glycoproteins are now cloned and sequenced and have been found to be members of major gene families, such as integrin, leucine rich glycoprotein (LRG), selectin, etc. In this chapter, the structure and the functions of membrane glycoproteins are briefly reviewed.