Book excerpt: Research in the matrix metalloproteinase field began with the demonstration by Gross and Lapière, in 1962, that resorbing tadpole tail expressed an enzyme that could degrade collagen gels. These humble beginnings have led us to the elucidation of around twenty distinct vertebrate MMPs, along with a variety of homologs from such diverse organisms as sea urchin, plants, nematode worm, and bacteria. This, coupled with four known specific inhibitors of MMPs, the TIMPs, gives a complex picture. Part I of Matrix Metalloproteinase Protocols provides the reader with a selective overview of the MMP arena, and a chance to come to grips with where the field has been, where it is, and where it is going. I hope that this complements all of the methodology that comes later. Part II presents the reader with a diverse set of methods for the expression and purification of MMPs and TIMPs, bringing together the long and often hard-earned experience of a number of researchers. Part III allows the reader to detect MMPs and TIMPs at both the protein and mRNA level, whereas Part IV gives the ability to assay MMP and TIMP activities in a wide variety of circumstances.