This chapter begins with defining composite materials. The different types of composites—namely, fiber-reinforced polymers, metal-matrix composites, and ceramic-matrix composites—are thoroughly discussed. The coverage of the FRP composites includes the various matrix materials used, the types of reinforcements and their arrangement, and their physical and mechanical properties. Next, the various methods of fabricating FRP composites are explained, supplemented by discussing how the fabrication method affects the design features of a product. Basic fundamentals of micromechanics are covered and how they can be used to predict the properties of a composite if the properties of the two components are given. The other types of composites, such as metal-matrix, ceramic-matrix, and carbon-carbon composites, are also discussed in detail. The discussion in each case includes the types of matrixes, reinforcements, and fabrication methods.