The matrix metalloproteinases (MMPs) are a large family of enzymes that break down different components of the extracellular matrix. Their catalytic activity is dependent on the metal ion zinc. This issue of the Protein Profiles covers the sequence information, three-dimensional structures, activation, protein substrates, specificity requirements, inhibition, and biological roles of all the currently identified MMPs. The action of these enzymes must be carefully regulated. One way the cell does this is by releasing inhibitory molecules known as tissue inhibitors of metalloproteinases (TIMPs). This volume contains information on the sequences, three-dimensional structures, and biological roles of the four known TIMPs. Matrix metalloproteinases and TIMPs will therefore be an invaluable source of data for all researchers interested in MMPs and TIMPS.