The Mertz Library is sometimes called "the library hiding in a garden hiding in New York City." It is one of the largest botanical libraries in the world and the largest in America, with over half a million volumes in its general research collection alone. Use of the library is free and has been since its opening in 1881. The library was one of the first structures built on the grounds of the New York Botanical Garden. Its collection includes books and materials on history, anthropology, landscape, and building design, architectural history, ethnobotany, urban social history, environmental policy, including over 3,000 linear feet of archival materials. The Mertz Library holds both rare and historically important works, notably flower portraits by Pierre-Joseph Redouté and 19th-century American seed catalogs.