In 2014, an international, interdisciplinary group of experts came together under the auspices of the PISA Governing Board to consider a novel question: can an international assessment evaluate, the global competence of 15-year-old students? The experts recognized the need for data to understand how well students are prepared for life in multicultural societies, identify what works in global education and accelerate progress toward the United Nations' Sustainable Development Goals. Collaborating with the 79 countries participating in PISA, the group began to develop an assessment of global competence to be administered as part of the 2018 round of PISA. Assessing global competence in all its complexity requires a multi-method, multi-perspective strategy. The assessment strategy of global competence in PISA 2018 has two components: (1) a cognitive test; and (2) a set of questionnaires completed by students, principals, teachers, and parents. The PISA assessment of global competence will offer the first comprehensive overview of education systems' success in equipping young people to address global developments and collaborate productively across cultural differences in their everyday lives. The data will provide insights on which policy approaches to global education are most commonly used in school systems around the world, and on how teachers are being prepared to promote global competence. Education systems will thus learn from each other how to best adapt curricula, promote innovative teaching methods, and adjust teachers' training so as to facilitate the development of global competence. The results of the assessment can also stimulate innovation at the level of individual schools, as schools seek effective approaches to raise their students' global competence.