Spiral notch torsion testing (SNTT) utilizes an extremely innovative concept of testing round-rod specimens having a V-grooved spiral notch line with a 45° angle. This chapter discusses the validity of SNTT in determining the fracture toughness (KIC) as established at the Oak Ridge National Laboratory. In SNTT testing, the plane-strain condition and uniformity of stress are maintained at every point along the spiral notch line of the specimen. These unique features of SNTT also points toward another possible, though yet unexplored vista of the SNTT: the potential for evaluating KIC of the zone of lowest KIC in a specimen with microstructurally varied regions. Validation of the SNTT technique to determine KIC and KISCC (the threshold K for stress corrosion cracking, SCC) of microstructurally varied region of the same specimens will be particularly attractive for testing the specimens of weldments and determining the weakest link, such as the heat affected zone (HAZ), in industrial welds. The preliminary results of a collaborative research program of Monash University, US Naval Research Laboratory, Oak Ridge National Laboratory, and Defense Science and Technology Organization, for development and use of the novel SNTT technique for determination of threshold stress intensity for stress corrosion cracking, are also described in the chapter.