Interfaces in metal and ceramic composites differ from interfaces in polymer matrix composites inasmuch as: (i) fiber degradation due to chemical reaction with the matrix at processing temperatures is frequent and (ii) bonding at the interface is generally chemical in nature (i.e. features primary chemical bond formation across the interface). Elementary analysis of requirements placed on the interface for mechanical property optimization indicate that, for toughening by fiber debonding and pull-out, very weakly bonded interfaces are needed. Sufficiently weak interfaces can be obtained by using interfacial layers of materials such as graphite or boron nitride which feature strongly anisotropic chemical bonding. Several tough inorganic composite utilize such interfaces. With large fibers in ductile matrices, however, strong interfaces are desirable if the matrix can provide sufficient resistance to crack propagation.