Formation of an extracellular matrix is required for multi-cellular life. The extracellular matrix provides mechanical support for cells and tissues, allows for organization of cellular structures and serves as a rich source of signals that influence cell behavior. Cellular signals that emanate from the extracellular matrix include those of molecular origin, such as growth factors that are sequestered in the matrix and ECM proteins that interact with cellular receptors in their own right. Signals also include tension and mechanical forces that are sensed by cells within a particular tissue environment. Once considered a fairly inert, structural element of living tissues, the extracellular matrix is now appreciated as a dynamic tissue component that interacts with cells and is a driving force in many fundamental processes of cell biology.