This document describes the nature of the Third Assessment of Mathematics for the National Assessment of Educational Progress. Information about the first two assessments is provided to give background information and details on the framework for the third assessment. It is noted that objectives for the third assessment are based on the second, with revisions that reflect current content and trends in school mathematics. Information about the content domain is provided, with the six content categories discussed: numbers and numeration; variables and relationships; shape, size, and position; measurement; probability and statistics; and technology. Technology is measured by assessing the use of calculators and computer literacy. Five categories in the process domain are reviewed: knowledge, skill, understanding, application and problem solving, and attitudes towards mathematics. Questions to be answered within each of the process categories are listed. The first of two appendices lists advisory committee members and consultants. The second provides additional information on three assessment topics: attitudes, the calculator, and estimation skills. (MP)