The quest for structural materials that can operate at higher and higher temperatures remains a persistent challenge in materials science. To achieve major increases in service temperatures, e.g., for aerospace propulsion systems, ceramic- and intermetallic-matrix composites offer perhaps the best prospects, although their cost is often prohibitive for many applications. For this reason, much recent work has focused on their monolithic counterparts. Despite significant advances in the development of such monolithic ceramics and intermetallics for structural use, their widespread adoption has been severely limited by their generally low ductility and poor fracture toughness, particularly at lower temperatures. In addition, it is now appreciated that these materials can be susceptible to premature failure by cyclic fatigue.