An inviting glass street wall and a crown of skylights announce the new home of Harvard University Library’s Weissman Preservation Center for some of the rarest books in the world, Information Systems offices, and a street level bookshop. The site on Mt. Auburn Street, surrounded by historic Harvard social clubs and Sert’s Holyoke Center, is at the very heart of pedestrian activity and energetically protected by the Cambridge Historic Commission and neighborhood groups. To balance competing community desires for a building in scale and size suited to the character of the street, and the university’s need for the maximum usable area for its programs, we created a carefully calibrated building with four stories above grade and two stories below using concrete flat slab construction to minimize overall building height. The new building projects an image of lightness and openness with its finely scaled and proportioned window wall facing Mt. Auburn Street. Along the sidewalk, a canopy protects the bookstore, display vitrines, and bookstore entry. At the top floor, sculptural skylights bring daylight into the Preservation Center. A new through block landscaped pathway links Mt. Auburn Street and Winthrop Street beyond. Sustainable design thinking played a critical role in winning community approval. The use of a geothermal heating and cooling system eliminating noisy and unsightly roof top mechanical equipment was a key to success for neighborhood groups. The north facing window wall and generous skylights minimize artificial lighting load, provide an ideal environment for the activities of the Preservation Center, and create a lively and open face to the street. After an extended community review process, members of the Cambridge Historical Commission dubbed the project “ a little jewel box.”