This report is concerned with the development of an analytical system for calculating thermal stresses during welding and resulting residual stresses. The present analysis concerns only longitudinal stresses, that is, stresses in the direction parallel to the weld line. Computer programs developed in this study calculate both temperature and stress distribution during welding. Using these programs, an analysis was made of effects of welding parameters on thermal stresses during bead-on-plate welding of ASTM 2219-0 aluminum alloy. Important results are : (a) The maximum stress at the weld center is little affected parameters. However, the width of tensile residual stress zone is significantly affected by welding parameters, especially heat input. With an increased heat input, a wider residual stress zone is formed. (b) However, when a weld is made with very low heat input, considerably high tensile stresses are produced in area just behind the arc. (c) Fairly high compressive stresses occur in area ahead of the welding arc. Experiments were conducted. Temperature and strain changes were recorded during bead-on-plate welding of 2219-0 aluminum alloy plate, 30 inches long, 18 inches wide, and 1/4 inch thick. Measured temperature changes coincide well with calculated ones by assuming the arc efficiency, η, to be 0.7. As far as the general trend is concerned, measured longitudinal strains coincide fairly well with calculated ones. However, transverse strains and shearing strains reach considerable amounts in area near the welding arc. The current analysis is not adequate for studying complex stress changes in area near the welding arc.