The Progress in International Reading Literacy Study (PIRLS) is an assessment of the reading comprehension of students in their fourth year of schooling, measuring student performance on a combined reading literacy scale and on a literary subscale and informational subscale. PIRLS is conducted by the International Association for the Evaluation of Educational Achievement (IEA). This report compares the performance of U.S. students with their peers worldwide. It also examines how the reading literacy of U.S. fourth-grade students has changed since the first administration of PIRLS in 2001. Results are presented by student background characteristics (sex and race/ethnicity) and by contextual factors that may be associated with reading proficiency (school characteristics, instructional practices and teacher preparation, and the home environment for reading). (Contains 9 tables and 12 figures. Appended are: (1) Sample Items From PIRLS 2006; (2) Technical Notes; (3) PIRLS Technical Review Panel, United States; and (4) PIRLS Publications.)