Welded structures subjected to repeated loads often exhibit stable crack growth or fatigue. Fatigue cracking has not been limited to a single class of material or application. Reasons for these failures are numerous but in general may be linked to some shortcoming in the design process. Despite the long history associated with welded aluminum structures, comprehensive fatigue design specifications did not appear in a US code until 1986. Experimental results used in the development of this specification are based primarily on fatigue tests of small specimens. Limitations on the application of such data to large structures have been documented for steel. This specification is further constrained by the lack of provisions governing variable amplitude loadings. A study was undertaken in 1988 to examine some of the issues associated with the design of welded aluminum structures. Experimentation included material characterization aimed at the development of predictive models, residual stress measurements, fatigue testing of axial specimens and beams, and detailed examination of fracture surfaces. Results pertinent to the development of the next generation fatigue design provisions are examined.