The NCTM Addenda Series includes 22 resource books covering K-6, 5-8, and 9-12 levels. These books have been developed, written, and field-tested by mathematics educators, and provide teachers at each grade level with dynamic activities to support and realize the Standards documents. Teachers developing their own curriculum units, as well as those supplementing a textbook, have found the Addenda Series books to be very helpful. The books that focus on particular topics, Subject-Matter Books: Compilations from K-6, and the Middle and High School books, have been found to be remarkable for curriculum development teams; they are nicely sequenced and provide a comprehensive framework for developing conceptual understanding.