Abstract: The present invention relates to the discovery that the collagen 11a1 (Col 11A1) protein, and/or fragments thereof, may be used to modulate bone mineralization. In some embodiments, bone mineralization is promoted by the addition of Col 11A1 or a fragment thereof, by pharmaceutical compositions that increase the presence of Col 11A1, and in some embodiments, bone mineralization may desired to be inhibited by pharmaceutical compositions that interfere, impede, or inhibit Col 11A1. The invention includes compositions including a Col 11A1 polypeptide, or fragment and compositions including a nucleic acid that encodes a Col 11A1 polypeptide or fragment. The invention also provides methods and kits for using such polypeptides and nucleic acids to treat bone mineralization disorders, and promote bone growth and fracture healing.