The textbook covers the physical nature of the welding process, classification and description of the main welding methods are given, the basic laws and regulations of physical chemistry are briefly considered, welding heat sources, processes of heating and heat distribution under welding conditions, metallurgical processes during welding, issues of crystallization and technological strength, basic laws of formation of the structure and properties of welded joints for various metals and alloys, as well as issues of technological weldability of metals and the principles of choosing a welding method and modes for the manufacture of various welded structures.