Since 1973, the National Assessment of Educational Progress (NAEP) has gathered information about student achievement in mathematics. Results of these periodic assessments, produced in print and web-based formats, provide valuable information to a wide variety of audiences. They inform citizens about the nature of students' comprehension of the subject, curriculum specialists about the level and nature of student achievement, and policymakers about factors related to schooling and its relationship to student proficiency in mathematics. The NAEP Assessment in mathematics has two components that differ in purpose. One assessment measures long-term trends in achievement among 9-, 13-, and 17-year-old students by using the same basic design each time. This unique measure allows for comparisons of students' knowledge of mathematics since it was first administered in 1973. The "2013 Mathematics Framework" reflects changes from 2005 in grade 12 only; mathematics content objectives for grades 4 and 8 have not changed. Therefore, main NAEP trend lines from the early 1990s can continue at fourth and eighth grades for the 2013 assessment. Special analyses have also determined that main NAEP trend lines from 2005 can continue at 12th grade for the 2013 assessment. Taken together, the NAEP Assessments provide a rich, broad, and deep picture of student mathematics achievement in the United States. Results are reported in terms of scale scores and percentiles. These reports provide comprehensive information about what students in the United States know and can do in the area of mathematics. These reports present information on strengths and weaknesses in students' knowledge of mathematics and their ability to apply that knowledge in problem-solving situations. In addition, these reports provide comparative student data according to gender, race/ethnicity, socioeconomic status, and geographic region; describe trends in student performance over time; and report on relationships between student proficiency and certain background variables. NAEP Mathematics Achievement Level Descriptions are appended. A bibliography is included. (Contains 12 exhibits.)