The primary objective of this program has been to develop simple laboratory-type tests to evaluate the toughness of high strength sheet alloys and their complex welded joints at cryogenic temperatures. The tests employed for evaluating the toughness of sheet materials included notiched tensile shear tests of individual resistance spot welds, and tensile tests of simple fusion welds. These tests were conducted at 78, -100, -320, and -423 F. These data, as well as data obtained from tensile tests of the base metal, percent martensite determinations, and metallographic examinations of fractured coupons, were correlated with low-cycle, highstress fatigue data obtained on complex welded joints at 78, -320, and -423 F. The most consistant index of toughness was found to be the notched/unnotched tensile ratio. The test data are presented in tabular and in graphical form to air metallurgical and design engineers in the selection of materials for structural applications at cryogenic temperatures. The test data were reduced by statistical methods and analzed. The results of the statistical analysis, which included means, standard deviations, and statistical values are presented and their importance discussed. A description of the test equipment and experimental procedures for tensile and fatigue testing at room and cryogenic temperatures is given. This report also includes conclusions, recommendations for future work, and references.