[en] The low-upper-self (LUS) toughness issue has a long history, beginning with the choice of materials for the submerged arc welding process, but also potentially involving the use of A302-B plate. Criteria for vessels containing LUS materials have usually been expressed in terms of the Charpy upper-shelf impact energy. Although these criteria have had several different bases, the range of limiting values for wall thicknesses approaching 229 mm (9 in.) has remained between 54 to 68 J (40 to 50 ft-lb). Values for vessels with thinner walls and/or only circumferential LUS welds could be less. A decision on criteria to be incorporated into the American Society of Mechanical Engineers Boiler and Pressure Vessel Code is approaching. Choices to be made concern the method for estimating the decrease in upper-shelf impact energy, flaw geometry for circumferential welds, statistical significance of toughness values, the choice between J_D and J_M, reference pressure, safety factors, and the inclusion of instability pressure calculations by means of R-curve extrapolation. Nuclear Regulatory Commission research programs have been and are contributing significantly to the resolution of the LUS issue. These programs embrace all aspects of the issue, including material characterization, large-scale testing, analysis, and criteria development. This report presents a comprehensive overview of the issue, including history and recommendations for expediting its resolution. 69 refs., 16 figs., 2 tabs