The healing of cracks in metallic components fundamentally involves the exchange of material and energy within an open system. The processes involved include welding and laser repair, various heat-treating techniques, hot plastic deformation, plasma spraying, electro-healing, electroplating, gas carbonitriding, friction stir welding, electric current-pulsing, thermo-mechanical coupling, filling of cracks via oxide formation, flash hot isostatic pressing, and various ultrasonic methods. The book describes the various techniques, their advantages and disadvantages.