Matrix metalloproteinases (MMPs) are a group of mammalian enzymes that in concert can degrade practically all extracellular matrix protein. They are also acknowledged important in the regulation of cell and tissue homeostasis, as they can degrade and modify several signaling molecules, e.g. cell surface receptors and growth factors. In hard tissues several MMPs are present, and the importance of some of them in the normal skeletal and dental development is well recognized. Still, the exact mode of function is not completely clear, as their expression and function seem to vary e.g. according to the location. Even though several other MMPs are also expressed in hard tissues, the current data has not been able to demonstrate their functional significance. This may be because their role is not absolutely essential to the normal growth and development of the calcified tissues. Alternatively, in the case of absence their function may be covered by other MMPs, as the substrate specificities of these enzymes are overlapping. This review concentrates on those MMPs which are known to have functional role in hard tissue formation, mineralization and/or remodeling.