Pathogenic specialization in the stripe rust pathogen Puccinia striiformis f. sp. tritici (Pst) has been conducted in many of the world’s cereal-growing regions since the 1930s. These studies used wheat genotypes that varied in their responses to rust isolates to classify isolates of Pst into physiologic races. As knowledge of the genetic basis of resistance in these wheat genotypes has improved, races (pathotypes) are now classified based on virulence for specific resistance genes rather than differential genotypes. Procedures for pathotype identification used at the University of Sydney’s Plant Breeding Institute are detailed, along with an explanation of how this information is linked to controlling stripe rust in farmer’s fields.