This is a subject which during recent years has aroused considerable interest in all industries and particularly in the aircraft industry and a large amount of investigation work has been carried out. In some industries, both light and heavy, the growth of welding as a “ production tool ” has been phenomenal, and the same growth is at the present time occurring in the structural steel work and shipbuilding industries. If one views this change which is taking place it will be observed that the change is entirely at the expense of riveting and bolting, and before proceeding I will roughly summarise the general disadvantages of these two processes.