The Morgan Library & Museum is composed of several structures. The main building was designed by Charles McKim of the firm of McKim, Mead and White, with an annex designed by Benjamin Wistar Morris. A 19th-century Italianate brownstone house at 231 Madison Avenue, built by Isaac Newton Phelps, is also part of the grounds. The museum and library also contains a glass entrance building designed by Renzo Piano and Beyer Blinder Belle. The main building and its interior is a New York City designated landmark and a National Historic Landmark, while the house at 231 Madison Avenue is a New York City landmark.