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. 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. The main NAEP Assessment is based on a framework (such as this one) that can be updated periodically. The "2011 Mathematics Framework" only reflects changes in grade 12 from 2005; 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 2011 assessment. In broad terms, this framework attempts to answer the question: What mathematics skills should be assessed on NAEP at grades 4, 8, and 12? Of critical importance is the fact that this document does not attempt to answer the question: What (or how) mathematics should be taught? The framework was developed with the understanding that some concepts, skills, and activities in school mathematics are not suitable to be assessed on NAEP, although they may well be important components of a school curriculum. This framework describes a design for the main NAEP assessments at the national, state, and district levels, but it is not the framework for the long-term trend NAEP Assessment. This report contains five chapters: (1) Overview; (2) Framework for the Assessment; (3) Mathematical Complexity of Items; (4) Item Formats; and (5) Design of Test and Items. NAEP Mathematics Achievement Level Descriptions is appended. A bibliography is included. (Contains 12 exhibits.) [The following people were the primary authors of the introductions to the content areas: Roger Howe; Richard Scheaffer, and Mary Lindquist.]