Saint Joseph's Oratory of Mount Royal (French: Oratoire Saint-Joseph-du-Mont-Royal) is a Roman Catholic minor basilica and national shrine located at 3800 Queen Mary Road in the Côte-des-Neiges neighborhood on Mount Royal's Westmount Summit in Montreal, Quebec. It is a National Historic Site of Canada and is Canada's largest church, with one of the largest church domes in the world. Founded in 1904 by Saint André Bessette in honour of his patron saint, Saint Joseph, the Oratory is the product of numerous architects and thousands of workers in a process spanning six decades. With its monumental scale, Renaissance Revival facade and contrasting Art Deco interior, the Oratory is recognizable not just in Montreal but around the world, attracting more than 2 million visitors and pilgrims to its steps each year.

The Oratory is the highest building in Montreal, rising more than 30 metres above Mount Royal's summit, allowing it to be seen from many kilometres away. It is the only building that violates the height restriction under the municipal building code of Montreal, which limits the height of any building, including skyscrapers, from surpassing the height of Mount Royal.

Since 2018, the dome and lantern atop the Oratory have undergone a series of renovations expected to be completed in 2024 by architecture firms Atelier TAG and Architecture49. The C$80 million project will create safe access to the lantern which will allow for an unprecedented 360-degree view over the mountain of the city.

Saint André Bessette, C.S.C. (1845–1937), more commonly known as Brother André, was a religious brother and a member of the Congregation of Holy Cross who became internationally renowned as a miracle healer. Due to his reputation, in 1904 he was given funding to construct a small chapel on Mount-Royal across from Notre Dame College to operate out of. The small, Gothic Revival style chapel expanded four times over the next decade with the growing of Brother André's fame and the Congregation decided to fulfill his request to build a basilica in his patron saint, Saint Joseph's honor. The original chapel, measuring 4.5 meters by 5.5 meters still stands today, though it has since been relocated about a hundred meters away to make room for the massive basilica that stands today.

The first phase of the basilica’s construction involved architects Dalbé Viau (1881–1938) and Alphonse Venne (1875–1934) who had previously done work for the Congregation. From 1914 to 1916, Viau and Venne constructed the crypt church, with seating for 1,000, which still stands today and forms the base of the basilica where the massive collection of stairs ends. Between 1924 and 1927, the crypt and building up until the roof were completed in the Renaissance Revival style. Viau and Venne had wanted the dome of the Oratory to resemble that of St. Peter’s Basilica in Rome, and to be smaller than it actually is today; however, they never had the chance to see those plans through as construction was halted with the Great Depression.

In 1937, Dom Paul Bellot (1876–1944), born in France, was hired to work after the death of Venne; however, he was required to work through Canadian Lucien Parent (1893–1956) due to not being a registered architect in Quebec. He redesigned Viau and Venne's roof and dome entirely, making the dome significantly larger and modelling it to resemble the dome of Florence Cathedral. The construction of his large Oratory dome lasted four years and was completed in 1941 after involving thousands of workers.

From 1949 to 1951, architect Gilbert Moreau carried out alterations and improvements to the interior of Saint Joseph's Oratory, as well as to the adjacent monastery, and rearranged the sacristy in the basilica.

Composer Émilien Allard was the church's carillonneur from 1955 to 1975. For RCA Victor he released the LP album Carols at the Carillon of Saint Joseph's Oratory for which he wrote the arrangements.