SummaryIn the 21st century, the wheat stripe rust fungus has evolved to be the largest biotic limitation to global wheat production. New pathogen genotypes are more aggressive and able to infect previously resistant wheat varieties, leading to rapid pathogen migration across and between continents. We now know the full life cycle, microevolutionary relationships and past migration routes on a global scale. Current sequencing technologies have provided the first fungal draft genomes and simplified plant resistance gene cloning. Yet, we know nothing about the molecular and microevolutionary mechanisms that facilitate the infection process and cause new devastating pathogen races. These are the questions that need to be addressed by exploiting the synergies between novel 21st century biology tools and decades of dedicated pathology work. Contents Summary 1625 I. Introduction 1625 II. Wheat stripe rust can be controlled with genetics 1626 III. The Puccinia striformis f. sp. tritici life cycle enables genetic diversity and rapid adaptation 1626 IV. Puccinia striformis f. sp. tritici evolves and migrates rapidly on a global scale 1626 V. Puccinia striformis . sp. tritici genomes are highly heterozygous and encode over 1000 candidate effectors 1628 VI. Novel 21st century tools to provide insight into Puccinia striformis f. sp. tritici biology 1629 VII. Conclusion 1629 Acknowledgements 1630 References 1630