The American Museum of Natural History commands four blocks in a park-like site adjacent to Central Park on the upper west side of Manhattan. After a thorough analysis of the existing facilities, a master plan was developed to guide the Museum’s growth. The design, which the Landmarks Commission approved, was developed to relate to the existing 19th century buildings. The first phase of that plan was the restoration of Roosevelt Hall, a New York City Landmark. This magnificent room was restored to its original state. Circulation was enhanced by introduction of new admissions, information, and coat facilities. The second phase of the plan involved the consolidation and expansion of the existing library into a new eight-story, 52,500 s.f. building. Integrating with the fourth and fifth floors of the museum, which were renovated to contain reading rooms, work areas, and administrative offices, the new building houses library stacks in a compact storage system with a capacity of 800,000 volumes. The design for the library extension seeks to present a facade that harmonizes with and integrates architectural elements from the adjacent historic museum structures. The red brick and limestone materials and fenestration elements are similar to the original Vaux and Mould Wing. The overall height and cornice line of extension, as well as the horizontal alignment and proportions of the window openings, were studied carefully. The placement, mass, and scale of detail and materials of the extension resulted in a building that is visually integrated into the site and allows the existing buildings, as before to be seen from Columbus Avenue and Central Park. A renovation and upgrade of the Roosevelt Hall as well as refurbishment of the exterior plaza and entire first and second floor exterior has also been achieved.