Collagen is found in biologic systems as a supporting material for a wide variety of cells and membranes. Its fibrous nature is well suited to biologic plasticity in both strength and form. Its natural occurrence as the primary structural protein of animals suggests that it might be used as a structural element in “synthetic” biomaterials. The molecular nature of collagen and its biologic reactivity must be understood, however, before collagen biomaterials can be designed and fabricated. Over the past 20 years, a broad and detailed account of the molecular biology of collagen has become available. The present report will review some of this material, with special reference to those aspects important to the use of collagen as a biomaterial, and illustrate some of the uses that these materials can serve.