This chapter examines the following: the concept of composites, roles of the matrix and reinforcement in composites, a history of composites, composite types — engineering and advanced, markets, composites industry structure. In the broad sense, the term composite materials refers to all solid materials composed of more than one component wherein those components are in separate phases. The matrix is the continuous phase of the composite. Polymeric composites can be divided into two groups, advanced composites and engineering composites. Each class of company can be involved in more than one step in the overall composites business. For instance, the raw material suppliers, especially the resin manufacturers, are often involved in compounding. This is especially true with fiber reinforced thermoplastics. Some raw material suppliers are also involved in making sheet and bulk molding compounds and prepregs.