The enhancement of engineering materials by surface modification has extended the operational envelope for many structures in terms of resistance to corrosion, wear, fatigue, and other forms of surface degradation and has made feasible the introduction of novel materials into high-performance applications. Surface engineering, using thermal-spray coatings, represents a pragmatic and highly costeffective means of satisfying stringent design criteria (e.g., in aerospace applications), operating under extreme environments (e.g., high temperatures, wear, and corrosion), and introducing a multiplicity of functions (e.g., thermal barriers, biomedical implants, and electronic multilayers). Thermal-spray technology as a family of processes is distinguished by its ability to deposit overlays of metals, ceramics, polymers, and composites of these materials in layers of substantial thickness (e.g., >25 µm) for engineering applications, often with equipment that can operate in the atmosphere and can be portable for use in the field. While traditional applications of thermal-spray coatings have addressed issues of surface protection, there is a growing activity in the use of the basic technology concepts for producing engineered functional surfaces and devices that offer the materials engineer a new scale of construction between thin films and macroscopic structures.