Collagen, the major extracellular matrix component, comprises a family of closely related, yet genetically distinct proteins that provide physiologic tensile properties to the tissues. The recent progress made in understanding the normal biochemistry and biology of collagens has permitted us to identify different levels at which errors might be introduced into the structure and metabolism of this protein. Several acquired and heritable diseases are now known to involve distinct abnormalities in collagen. This conference reviews some of the latest discoveries in the biochemistry of collagen and highlights some disease entities in which definitive information on molecular alterations in collagen is available.