Matrix metalloproteinases (MMPs), also known as matrixins, belong to a group of zinc-dependent proteins, which are thought to play a central role in the breakdown of extracellular matrix. Collagen, elastin, gelatin and casein are major components cleaved by MMPs. The breakdown of these components is essential for many physiological processes such as embryonic development, morphogenesis, reproduction, and tissue resorption and remodelling. MMPs also participate in pathological processes such as arthritis, cancer, cardiovascular and neurological diseases. This review summarizes current knowledge regarding these proteins, their participation in physiological and pathophysiological roles, their involvement in activation and inhibition, and their interactions with other metal-binding proteins including metallothioneins.