The matrix metalloproteinases (MMPs) are a family of homologous zinc endopeptidases. Increased degradation of extracellular matrix macromolecules is a central event in the disease process of illness such as arthritis Matrix metalloproteinases are important enzymes found in connective tissues and thought to be involved in cartilage degradation. The current view is that the initial step in the breakdown of the matrix in physiology and pathological situations is an extracellular process, often involving malrix metalloproteinases. They are detectable in synovial fluids and may play a destructive role in septic arthritis. In this review, it is introduced that the members of the MMP family and describe their structural features, substrate specificities, general features of the activation mechanism, and the involvement of tissue inhitors of metalloproteinases in the activation process.