The tissue inhibitors of metalloproteinases (TIMPs) are naturally occurring proteins that specifically inhibit matrix metalloproteinases and regulate extracellular matrix turnover and tissue remodeling by forming tightly bound inhibitory complexes with the MMPs. Thus, TIMPs maintain the balance between matrix destruction and formation. An imbalance between MMPs and the associated TIMPs may play a significant role in the invasive phenotype of malignant tumors. TIMP proteins share several structural features including six loops held in place by six disulfide bonds arranged in three knotlike structures. The N terminal region is necessary for inhibitory activity. The N terminus of each TIMP contains a consensus sequence (VIRAK) and each TIMP is translated with a 29 amino acid leader sequence that is cleaved to produce the mature protein. The C terminal regions are divergent and enhance the inhibition selectivity and binding efficiency. Although the TIMP proteins share high homology, following secretion they are localized extracellularly either in soluble form (TIMP1, TIMP2, and TIMP4) or bound to extracellular matrix components (TIMP3).