Extracellular Matrix (ECM) are collection of extracellular molecules secreted by cells that provides structural and biochemical support to the surrounding cells. They are substances containing Collagen, Elastin, Proteoglycans, Glycosaminoglycans and fluid produced by the cells they are embedded. They fill the spaces between the cells in a tissue protecting them and holding them together. They are the natural support Structures of the cells. The extracellular matrix may be semifluid or rigidly solid and hard as in bone. Each type of connective tissue in animals has a type of ECM: collagen fibers and bone mineral comprise the ECM of bone tissue; reticular fibers and ground substance comprise the ECM of loose connective tissue; and blood plasma is the ECM of blood. Some common function of the Extracellular Matrix includes cell adhesion; cell-to-cell communication and cell differentiation.