Naturalis Biodiversity Center (Dutch: Nederlands Centrum voor Biodiversiteit Naturalis) is a national museum of natural history and a research center on biodiversity in Leiden, Netherlands. It was named the European Museum of the Year 2021.
Although its current name and organization are relatively recent, the history of Naturalis can be traced back to the early 1800s. Its collection includes approximately 42 million specimens, making it one of the largest natural history collections in the world.
 The beginnings of Naturalis go back to the creation of the Rijksmuseum van Natuurlijke Historie (abbreviated RMNH, National Museum of Natural History) by Dutch King William I on August 9, 1820. In 1878, the geological and mineralogical collections of the museum were split off into a separate museum, remaining distinct until the merger of the Rijksmuseum van Natuurlijke Historie with the Rijksmuseum van Geologie en Mineralogie (abbreviated RGM) in 1984, to form the Nationaal Natuurhistorisch Museum (NNM) or National Museum of Natural History.
 In 1986, it was decided that the institution should become a public museum, and a new building was designed by the Dutch architect Fons Verheijen. The building's reception area incorporated the 1657-1661 Pesthuis, designed by Huybert Corneliszoon van Duyvenvlucht. Completed in 1998, it was opened on April 7, 1998, by Queen Beatrix of the Netherlands. The new building costs were about €60 million, making it the second most expensive museum building in the Netherlands.[citation needed]
 In 2010 the National Museum of Natural History (Naturalis) further combined with the Zoological Museum Amsterdam (ZMA) of the University of Amsterdam, and the Dutch National Herbaria at the universities of Leiden, Amsterdam and Wageningen, to form the Nederlands Centrum voor Biodiversiteit (NCB Naturalis). The combined institute was formally opened as part of the ‘International Year of Biodiversity 2010’ by Education Minister Ronald Plasterk and Agriculture Minister Gerda Verburg.
 In 2012 the name became the Naturalis Biodiversity Center. Naturalis has partnered with ETI Bioinformatics in support of the Catalog of Life (CoL), and is working with the Global Biodiversity Information Facility.
Funding is in place to support digitization of the massed collections.
In 2015, further renovation and expansion was planned, with a proposed design from Neutelings Riedijk Architecten. The Pesthuis (historical Plague hospital) will no longer be part of the complex.  However, a lawsuit by the previous architect postponed these plans. The museum, except the research facilities, was closed from September 2018 to mid 2019 due to renovations. Temporary exhibitions were held in the Pesthuis, the former entrance building, during the renovations. The new building was finished in the summer of 2019 with the museum opening again on August 31 of that year.
 Within a year of the opening the museum had to close again in March 2020 due to the COVID-19 pandemic until June 2020. The museum reopened on June 8 with free entrance for essential workers. On July 1 the museum was reopened for the public charging full prices again. It closed again in the winters of 2020 and 2021 due to further national COVID-19 measures.
 Naturalis was named the European Museum of the Year 2021 in the annual awards of the European Museum Forum. The jury cited Naturalis as "a very inventive museum with beautiful exhibitions",  and also that the museum's "agile ability" to move on and transform itself.
 The current museum is known for the numerous objects in its collections. Prior to the merger with the Zoölogisch Museum Amsterdam and National Herbarium of the Netherlands, there were approximately 10 million zoological and geological specimens in the Naturalis collection. Following the merger with the collections of the Zoölogisch Museum Amsterdam and National Herbarium of the Netherlands in 2010–12, there are now approximately 42 million specimens:
 The largest part of the collections are stored in a 60-meter-high tower, a landmark in Leiden, opened in April 1998. Some parts of the collections are stored in a depot in the former museum building at the Raamsteeg in the city center of Leiden.
 The Index Herbariorum code assigned to Naturalis is L and it is used when citing housed herbarium specimens.
 Among the collections at Naturalis are the papers and field notes of a number of early travelers and naturalists, including the following:
 The museum has several permanent exhibitions:
 During the renovation of the main building the former entrance building, the historic Pesthuis, was used for three temporary exhibits from 2016 to 2018.
 During the COVID-19 pandemic the museum was made virtually accessible. The visitor can move freely through the exhibitions with information and short videos available in Dutch or English to add context to some of the museum's highlights.
 Besides its role as a museum, Naturalls is also a scientific research institute collaborating with most Dutch universities. Around 120 researchers and 200 guest researchers are working at Naturalis in nine groups on topics such as biodiversity, botany, marine biology, or geology. Naturalis is a (co-)initiator of several citizen science projects. With the project Arise, which aims to map all biodiversity in the Netherlands, Naturalis is a player in one of the largest Dutch research infrastructure projects.
 Naturalis had an estimated 285,000 visitors and was the 15th most visited museum of the Netherlands in 2013. The museum had a record number of 339,550 visitors in 2015.