This chapter presents discussion of devoted to a survey of the structural features, tissue distribution, and potential specialized functions of the various collagens. It emphasizes selectivity with respect to tissue distribution and cellular origin. The relatively large number of collagen chains plus numerous posttranslational modifications of the chains and molecules derived from them generate enormous diversity in the chemical and structural characteristics of the collagen family of proteins. Type X collagen represents an additional apparently cartilage-specific collagen composed of relatively short chains. The properties of the various collagens specify the molecular architecture of the aggregates. Type IV collagen is a major macromolecular constituent of basement membranes and can be readily isolated from basement-membrane-rich tissues or highly vascularized tissues such as the placental villi. This collagen appears to be largely restricted to structures identifiable as basement membranes. Type IX and X collagens constitute additional minor collagenous constituents of hyaline cartilages.