This book is a guide for applying fundamental knowledge of welding metallurgy and weldability principles to the practical selection of materials, welding processes and process parameters, and post-weld processing to optimize weld properties and performance. It also provides insight into conducting failure analysis of welded lightweight alloy structures. This is followed by an in-depth discussion of the influence of alloy chemical composition, welding process and associated thermal cycles on weld solidification, solid-state phase transformations, microstructure evolution and mechanical properties. The origin and prevention of weld defects such as porosity are also presented. In addition, the book provides insight into conducting failure analysis of welded lightweight ally structures.