Technological peculiarities of the formation of the structure and properties of black and non-ferrous structural materials under the thermal and deformation effect of the fusion welding process on them are considered. The relationship between the technological strength of welded joints and the initial phase state of the welded materials and the degree of change in their mechanical and special properties during welding is shown. This makes it possible to implement various approaches to the design of welding technology in order to obtain the required quality and operational characteristics of welded structures. The tutorial has been developed in accordance with the requirements for the training of a welding engineer of international qualification (IWE) in accordance with the IAB-002-2000EWF-409SY-2 guidance document and can be used to study the courses "Theory of welding processes" and "Fundamentals of fusion welding."