The extracellular matrix provides an environment for cells. It is produced, assembled, and modified by cells and in turn, it modifies the functions and behavior of the cells it encounters. The molecules that make up the matrix are diverse in both structure and function. This well-illustrated unit provides an introduction to the structure and function of the major components of the extracellular matrix and serves as a background for the other units in the chapter, which include protocols for isolation and analysis of individual components.