This National Academy of Education (NAEd) volume provides guidance to key stakeholders on how to accurately report and interpret comparability assertions concerning large-scale educational assessments as well as how to ensure greater comparability by paying close attention to key aspects of assessment design, content, and procedures. The goal of the volume is to provide guidance to relevant state-level educational assessment and accountability decision makers, leaders, and coordinators; consortia members; technical advisors; vendors; and the educational measurement community regarding how much and what types of variation in assessment content and procedures can be allowed, while still maintaining comparability across jurisdictions and student populations. At the same time, the larger takeaways from this volume will hopefully provide guidance to policy makers using assessment data to enact legislation and regulations and to district- and school-level leadership to determine resource allocations, and also provide greater contextual understanding for those in the media using test scores to make comparability determinations.