This review critically examines 33 studies on students' epistemological beliefs about mathematics. Five categories were identified: beliefs about mathematics, development of beliefs, effects of beliefs on behavior, domain differences, and changing beliefs. Studies examining beliefs about mathematics revealed consistent patterns of nonavailing beliefs at all educational levels. Mathematics instructional environments were inferred to influence the development of beliefs about mathematics. All studies revealed significant relationships between beliefs and cognition, motivation, and academic achievement. Descriptive studies found relationships between beliefs and learning behaviors. Studies examining domain differences found significant variations in beliefs across disciplines. Studies focusing on changing beliefs were successful, which was attributed to appropriate changes in instructional style. The article concludes with suggestions for future research.