Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that function to maintain and remodel tissue architecture. Their substrates represent an astounding variety of extracellular matrix components, secreted cytokines and cell surface molecules, and they have been implicated in a wide range of processes and diseases. To date MMPs have been found in virtually every tissue of the eye under conditions of health and disease. Although their functions in vivo remain poorly understood, it is clear they impact on essentially every aspect of eye physiology. This chapter reviews the expanding literature on MMPs in the eye and attempts to place it in the context of basic MMP biology. A general overview of MMP functions is presented first, and then the discussion moves to examples of possible MMP roles in two eye structures. For the cornea, we present recent work on the roles of MMPs during various aspects of wound healing. For the retina, we describe the activities of MMPs in specific disease states from which common principles may emerge.