The ROM began as an extension of the University of Toronto, formally established on April 16, 1912, and opened to the public on March 19, 1914, by the Duke of Connaught. The original building, designed by Frank Darling and John A. Pearson, was a synthesis of Italianate and Neo-Romanesque styles - heavy massing, arched windows, decorative eave brackets meant to convey monumentality. In its early decades, the museum functioned primarily as a collecting institution, not an exhibiting one. Insects were pinned in long rows of glass cases with only species names for description. Specimens sat in Edwardian arrangements that changed little for decades. The transformation came gradually through the 1960s, when dinosaur fossils began appearing in dynamic poses against painted landscapes, and the galleries shifted from static taxonomy to interpretive storytelling. By the 1980s, the Bat Cave exhibit was using strobe lights and puffs of air to simulate walking through a Jamaican cave as bats flew overhead.

In 2002, the ROM embarked on Renaissance ROM, a massive renovation anchored by Daniel Libeskind's crystalline addition. Michael Lee-Chin donated $30 million; the Ontario and Canadian governments contributed $60 million more. The result was the Michael Lee-Chin Crystal, opened on June 2, 2007 - a deconstructivist form clad in 25 percent glass and 75 percent aluminum, its canted walls deliberately avoiding contact with the heritage buildings behind it. Globe and Mail critic Lisa Rochon wrote that the new ROM "rages at the world" and called it oppressive. Toronto Star's Christopher Hume championed it as a monument. The steel framework was fabricated in Hamilton, Ontario; the anodized aluminum cladding came from Josef Gartner in Germany, reportedly the only company capable of producing it. Water leakage plagued the structure by October 2007, drawing comparisons to Libeskind's Denver Art Museum, which suffered similar problems. Love it or loathe it, the Crystal made the ROM impossible to ignore.

The ROM's natural history collections stretch from the Precambrian to the present. The Willner Madge Gallery traces the evolution of life from the Burgess Shale's Cambrian explosion to the Triassic, featuring specimens from two of Canada's most significant fossil sites - the Burgess Shale in British Columbia and Mistaken Point in Newfoundland. Gordo, one of the most complete Barosaurus specimens in North America, dominates the dinosaur galleries as the largest dinosaur on display in Canada. A Zuul crurivastator skeleton - one of the most complete ankylosaurid specimens ever found - adds to the collection's scientific weight. The Teck Suite of Galleries houses nearly 3,000 specimens of minerals, gems, and meteorites, including fragments of the Tagish Lake meteorite and the Light of the Desert, the world's largest faceted cerussite. The Schad Gallery of Biodiversity displays specimens of species both endangered and extinct - a dodo skeleton, a great auk, a passenger pigeon - alongside Bull, the southern white rhinoceros whose survival became a conservation success story.

The world culture galleries span continents and millennia. The Bishop White Gallery holds three of the best-preserved Yuan dynasty temple wall paintings in existence, dating to around 1298-1300. The ROM Gallery of Chinese Architecture houses one of the largest collections of Chinese architectural artifacts outside of China, including the Tomb of General Zu Dashou and a reconstruction of an Imperial Palace building from Beijing's Forbidden City. The Wirth Gallery of the Middle East displays over 1,000 artifacts from the Fertile Crescent, among them the Striding Lion from King Nebuchadnezzar II's throne room in Babylon. The Gallery of Africa: Egypt holds the gilded sarcophagus and mummy of Djedmaatesankh, a female musician at the temple of Amun-Re in Thebes. Canada's own story appears in the Daphne Cockwell Gallery, where more than 1,000 First Peoples artifacts include the important Heiltsuk collection acquired between 1899 and 1906, and Nisga'a and Haida crest poles wind around the central staircase.

The ROM attracts more than one million visitors annually, making it the most-visited museum in Canada and the second-largest in the country. The subway station bearing its name was renovated in 2008 to display reproductions of the museum's collection at platform level - a reminder that in Toronto, you encounter the ROM before you even reach it. Renovations begun in 2024 are correcting the Crystal's architectural deficiencies while respecting Libeskind's original vision, expanding the atrium skylight for natural lighting and rebuilding the entrance plaza to allow street performances. The museum remains Canada's largest field-research institution, with conservation activities spanning the globe. What opened in 1914 as a university annex where insects were pinned in silent rows has become a place where four and a half billion years of Earth's story meets one of the most argued-about buildings of the twenty-first century.