In biology, extracellular matrix (ECM) is any material part of a tissue that is not part of any cell. Extracellular matrix is the defining feature of connective tissue.

ECM's main component is various glycoproteins. In most animals, the most abundant glycoprotein in the ECM is collagen. ECM also contains many other components, proteins such as fibrin and elastin; minerals such as hydroxyapatite ; or fluids such as blood plasma. Given this diversity, it can serve any number of functions.

Many cells bind to components of the extracellular matrix. This cell-to-ECM adhesion is due to specific cell surface adhesion proteins.