The numerous functions of the knee joint are based on a finely coordinated interaction of diverse elements of the locomotor system, including the articular cartilage, tendons, and ligaments. These tissues owe their unique biomechanical properties to the presence of specific macromolecules in the extracellular space, their organization into higher-order structural units, and the interactions among them. The macro- and supramolecular organization of the extracellular matrix in these tissues remains under cellular control throughout the life of the individual. This is of crucial importance as it relates to the ongoing “transformation and renewal” of tissues and to possible regenerative processes.