Welding thick section materials in the vertical or near vertical position between retaining shoes is presently done by two related procedures, electroslag welding and electrogas welding.Each of these processes is characterized in this report, with emphasis on fundamentals such as the heat flow conditions, metal transfer, weld pool morphology, and chemical and electrochemical aspects of the slag and weld pool reactions.Primarily applied for joining steels of thicknesses over 50 mm (2 in.), electroslag welding involves high energy input relative to other welding processes resulting in inferior mechanical properties, specifically low toughness of the heat-affected zone.Where a postweld heat treatment can be applied this problem is overcome.