The extracellular matrix (ECM) serves as a medium for cell-cell interactions and can directly signal cells through cell surface ECM receptors, such as integrins. In addition, many growth factors and signaling molecules are stored in the ECM. Thus, ECM remodeling and/or degradation plays a critical role in cell fate and behavior during many developmental and pathological processes. ECM remodeling/degradation is, to a large extent, mediated by matrix metalloproteinases (MMPs), a family of extracellular or membrane-bound, Zn2+-dependent proteases that are capable of digesting various proteinaceous components of the ECM. Of particular interest among them is the MMP11 or stromelysin-3, which was first isolated as a breast cancer associated protease. Here, we review some evidence for the involvement of this MMP in development and diseases with a special emphasis on amphibian metamorphosis, a postembryonic, thyroid hormone-dependent process that transforms essentially every organ/tissue of the animal.