This study summarizes the initial two-year project sponsored by the American Iron and Steel Institute in which way of improving the fatigue resistance of electrical resistance spot welds were sought. Both low-carbon and HSLA steels were considered. Testing was limited to the tensile-shear weld geometry.Both galvanized and bare sheet steel were used.Improvement techniques considered were: control of residual stresses, control of weld geometry, increasing base metal strength, and state of the steel sheet surface.The most important result of this study was to show that the fatigue resistance of tensile-shear spot welds (particularly HSLA) could be greatly improved by treatments which either reduced the tensile residual stresses resulting from welding or induced compressive residual stresses at the critical notch-root site of crack initiation and early growth.The improvements possible through modification of weld geometry were smaller than those possible through control of residual stresses except for the improvements resulting from the reduction of joint rotation as shown by Davidson.Increasing the base metal tensile strength did not greatly alter the fatigue resistance of as-welded tensile-shear spot welds presumably because such increases are off-set by higher (tensile) residual stresses.The state of the steel sheet surface, that is, galvanized or bare, had little if any influence on the test results.