Since 2016 an international research process has been underway to design and develop an international geography assessment for implementation in lower secondary education settings. One of the crucial steps in this process is the development and validation of an assessment framework that models the content and cognitive dimensions of geography education to enable internationally valid, reliable, and fair measures of geographic constructs. This paper provides a rationale for an international assessment in geography and reports the findings of foundational research that produced the provisional assessment framework. Our methodology draws on the evidence-centered design to educational assessment development, which involves a sequential approach to domain analysis and modelling. The framework will guide the specifications for tasks and tests, evaluation procedures, and measurement models. The article concludes with a reiteration of the value of an international assessment and an outline of the activities moving forward.