Welding Metallurgy by Sindo Kou has been used worldwide as a reference book for welding practitioners and researchers since it was published in 1987. The third edition provides many updated features including a simple criterion for predicting effect of filler metals on liquation cracking, an index and analytical equations for predicting susceptibility to solidification cracking, a test for evaluating susceptibility to solidification cracking and filler-metal effect, and more. New topics touched on by the author include weldability of magnesium alloys, friction stir welding, and transport phenomena such as surfactant effect on flow oscillation, metal-vapor effect on arc temperature and weld shape, and spatter.