Assessment is one of the most discussed topics in mathematics education today. Issues drawing particular attention include the proper role of formative assessment, the need to show accountability through large-scale assessment, and the use of assessment to measure student learning of the content and practices in evolving new standards. The 2015 issue of Annual Perspectives in Mathematics Education (APME) approaches assessment from a wide variety of perspectives. Its 21 chapters, written by leading mathematics educators and researchers, are grouped into four sections: Assessment in ActionDesign of Assessment Tools and StrategiesProfessional Learning to Enhance Classroom AssessmentAssessment as Reasoning from EvidenceThe chapters in this volume include descriptions of research projects, classroom examples, research observations, and proven strategies that teachers can readily use. A concluding chapter by Dylan Wiliam surveys the many ideas and issues that the authors address and places them in today's complex assessment landscape. Through the wide-ranging research that this year's issue of APME presents, it is intended to support educators at all levels as they develop and use assessment to improve the teaching and learning of mathematics for all students.