Fundamental issues related to the technological foundations of fusion welding of metals, alloys, dissimilar metals, as well as some features of welding heating plastics are considered. Technological bases of processes of manual arc welding with coated electrodes, non-consumable electrode are described; semi-automatic consumable electrode welding; automatic submerged arc welding; electroslag welding of metals and staves; technological features of welding polymer materials and products. Significant attention is paid to the processes of welding of various welded and structures, flaw formation in welds and joints, as well as methods for its reduction and control. Safety and health issues during electric arc welding are covered in sufficient detail.