The results of a number of investigations on the properties of 5083-0 plate and weldments of various thicknesses have been summarized. The data show that the tensile properties and toughness of 5083-0 plate at room and subzero temperatures remain about constant or decrease modestly with an increase in thickness from 1 to 9 in. and that the properties of 5083-0 plate formed into a spherical contour by the Alcoa 570 process are essentially the same as those of asrolled 5083-0 plate. Both strength and toughness are higher at -260 and -320°F than at room temperature. The strength and toughness of 5183 welds at room temperature, -260, and -320°F are equivalent to those of the parent plate. The high toughness of these products at those temperatures has been demonstrated by tests of relatively large-scale specimens, all of which have fractured by ductile tearing; conservative engineering estimates of KIc and Kc have been made based upon these results and those published in the literature. The fatigue crack propagation characteristics of these materials have been established and found to be largely unaffected by temperature, thickness, orientation, or location in the weld. Crack growth rates are faster in moist air than in dry air.