Background: Data use has been promoted as a panacea for instructional improvement. However, the field lacks a detailed understanding of how teachers actually use assessment data to inform instruction and the factors that shape this process. Purpose: This article provides a review of literature on teachers' use of assessment data to inform instruction. We draw primarily on empirical studies of data use that have been published in the past decade, most of which have been conducted as data-driven decision making came into more widespread use. The article reviews research on the types of assessment data teachers use to inform instruction, how teachers analyze data, and how their instruction is impacted. Research Design: Review of research. Findings: In the current accountability context, benchmark assessment data predominate in teachers' work with data. Although teachers are often asked to analyze data in a consistent way, agendas for data use, the nature of the assessments, and teacher beliefs all come into play, leading to variability in how they use data. Instructional changes on the basis of data often focus on struggling students, raising some equity concerns. The general absence of professional development has hampered teachers' efforts to use data, as well as their confidence in doing so. Conclusions: Given that interim benchmark assessment data predominate in teachers' work with data, we need to think more deeply about the content of those assessments, as well as how we can create conditions for teachers to use assessment to inform instruction. This review of research underscores the need for further research in this area, as well teacher professional development on how to translate assessment data into information that can inform instructional planning.