It was only 2 years ago that “Collagen and Gelatin in the Solid State” was discussed by Yannas [1] in this Journal. That another review follows so soon is a reflection of the breadth of the subject and the accelerating interests in this field. Unlike other biological macromolecules which have specific genetic or metabolic activities, collagen belongs to a class of structural proteins. It is ubiquitous in the animal kingdom, contributing 20 to 30% of total body proteins in vertebrate. It is present throughout the body but is in high concentration in skin, tendon, and bone. As the characteristic extracellular component of the mesodermal tissue, collagen occupies a key position in the molecular architecture of higher animals which enables it to be the main agent controlling the distribution of both external and internal forces. For these reasons, collagen research has brought together biologists, physiologists, chemists, physicists, and engineers in an interdisciplinary endeavor.