This document contains the design and rationale for assessing science achievement of students throughout the United States in 2005. This same Framework has been used by NAEP for the 1996 and 2000 science assessments. The Framework provides a general overview of NAEP, describes the NAEP Science Framework adopted by NAGB, and reviews the process by which the Framework was developed. Appended are: (1) NAEP Science Achievement; (2) Fields of Science; (3) Examples of Themes by Grade Level; (4) Science Content Outlines (Excerpts); and (5) Science Committees and Project Staff. A list of selected readings is also provided.