The plant extracellular matrix (ECM) includes a variety of proteins with critical roles in the regulation of plant growth, development, and responses to pests and pathogens. Several studies have shown that various ECM proteins undergo proteolytic modification. In mammals, the extracellular matrix metalloproteinases (MMPs) are known modifiers of the ECM, implicated in tissue architecture changes and the release of biologically active and/or signalling molecules. Although plant MMPs have been identified, little is known about their activity and function. Plant MMPs show structural similarity to mammalian MMPs, including the presence of an auto-regulatory cysteine switch domain and a zinc-binding catalytic domain. Plant MMPs are differentially expressed in cells and tissues during plant growth and development, as well as in response to several biotic and abiotic stresses. The few gene expression and mutant analyses to date indicate their involvement in plant growth, morphogenesis, senescence and adaptation and response to stress. In order to gain a further understanding of their function, an analysis and characterisation of MMP proteins, their activity and their substrates during plant growth and development are still required. This review describes plant MMP work to date, as well as the variety of genomic and proteomic methodologies available to characterise plant MMP activity, function and potential substrates.