The Royal Ontario Museum (ROM) is a museum of art, world culture and natural history in Toronto, Ontario, Canada. It is one of the largest museums in North America and the largest in Canada. It attracts more than one million visitors every year, making it the most-visited museum in Canada. The 74,000 square metres (800,000 sq ft) museum building is located north of Queen's Park, in the University of Toronto district, with its main entrance on Bloor Street West. Museum subway station is named after it and, since a 2008 renovation, is decorated to resemble the ROM's collection at the platform level; Museum station's northwestern entrance directly serves the museum.

Established on April 16, 1912, and opened on March 19, 1914, the ROM has maintained close relations with the University of Toronto throughout its history, often sharing expertise and resources. It was under direct control and management of the University of Toronto until 1968, when it became an independent Crown agency of the Government of Ontario. It is Canada's largest field-research institution, with research and conservation activities worldwide.

With more than 18 million items and 40 galleries, the museum's diverse collections of world culture and natural history contribute to its international reputation. It contains a collection of dinosaurs, minerals and meteorites; Canadian and European historical artifacts; as well as African, Near Eastern, and East Asian art. It houses the world's largest collection of fossils from the Burgess Shale in British Columbia with more than 150,000 specimens. The museum also contains an extensive collection of design and fine art, including clothing, interior, and product design, especially Art Deco.

The Royal Ontario Museum was formally established on April 16, 1912, and was jointly governed by the Government of Ontario and the University of Toronto. Its first assets were transferred from the university and the Ontario Department of Education, coming from its predecessor, the Museum of Natural History and Fine Arts at the Toronto Normal School. On 19 March 1914, the Duke of Connaught, also the governor general of Canada, officially opened the Royal Ontario Museum to the public. The museum's location at the edge of Toronto's built-up area, far from the city's central business district, was selected mainly for its proximity to the University of Toronto's St. George campus. The original building was constructed on the western edge of the property along the university's Philosopher's Walk, with its main entrance facing out onto Bloor Street housing five separate museums of the following fields: Archaeology, Palaeontology, Mineralogy, Zoology, and Geology. It cost CA$400,000 to construct. This was the first phase of a two-part construction plan intended to expand toward Queen's Park Crescent, ultimately creating an H-shaped structure.

The first expansion to the Royal Ontario Museum publicly opened on October 12, 1933. The CA$1.8-million renovation saw the construction of the east wing fronting onto Queen's Park and required the demolition of Argyle House, a Victorian mansion at 100 Queen's Park. As this occurred during the Great Depression, an effort was made to use primarily local building materials and to make use of workers capable of manually excavating the building's foundations. Teams of workers alternated weeks of service due to the physically draining nature of the job.

In 1947, the ROM was dissolved as a body corporate, with all assets transferred to the University of Toronto. The museum remained part of the University until 1968, when it, along with the newly opened McLaughlin Planetarium, was reincorporated as a single separate entity. The planetarium was named after benefactor Samuel McLaughlin, who provided CA$2 million for its construction.

The second major addition to the museum was the Queen Elizabeth II Terrace Galleries on the north side of the building and a curatorial centre built on the south, which started in 1978 and was completed in 1984. The new construction meant that a former outdoor "Chinese Garden" to the north of the building facing Bloor, along with an adjoining indoor restaurant, had to be dismantled. Opened in 1984 by Queen Elizabeth II, the CA$55 million expansion took the form of layered terraces, each rising layer stepping back from Bloor Street. The design of this expansion won a Governor-General's Award in Architecture.

In 1989, activists complained about its Into the Heart of Africa exhibit, which featured stereotypes of Africans, forcing curator Jeanne Cannizzo to resign.