This book, written primarily for the welding phase of the Aviation Structural Mechanic rating, deals with both oxy-acetylene and electric arc welding. The section devoted to the oxyacetylene method begins with an introduction to fundamental equipment, and is followed by practical instructions in welding techniques. Ensuing chapters deal with oxyacetylene cutting, brazing, soldering, and hand forging. The second section deals with arc welding, inert arc welding, and atomic-hydrogen welding. The discussions on arc welding begin with equipment and its operation, then move on to studies of the arc and electrodes. Information on factors governing arc welded joints and techniques of position welding follow. This section is concluded with a discussion of expansion, contraction, and distortion, and the arc welding of nonferrous metals. The chapter on inert arc welding briefly defines the process and discusses types, uses, and care of equipment and material. Simple jobs, including current setting, gas adjustment, and techniques involved in developing skills are also included. The chapter on atomic hydrogen welding discusses theory of operation, types of equipment, and various applications that are possible with this method of welding. A few practice examples are included to familiarize the student with welding processes and techniques.