The Bank of Montreal (BMO; French: Banque de Montréal) is a Canadian multinational investment bank and financial services company.

The bank was founded in Montreal, Quebec, in 1817 as Montreal Bank; while its head office remains in Montreal, the operational headquarters and executive offices have been located in Toronto, Ontario since 1977. One of the Big Five banks in Canada, it is the fourth-largest bank in Canada by market capitalization and assets, and one of the ten largest banks in North America. It is commonly known by its acronym BMO (pronounced ), which is also its stock symbol on both the Toronto Stock Exchange and the New York Stock Exchange. In October 2021, it had CAD$634 billion in assets under administration (AUA). The Bank Of Montreal swift code is BOFMCAM2 and the institution number is 001.On 23 June 1817, John Richardson and eight merchants signed the Articles of Association to establish the Montreal Bank in a rented house in Montreal, Quebec. The bank officially began conducting business on 3 November 1817, making it Canada's oldest bank. It underwent a name change to its current in 1822. BMO's Institution Number (or bank number) is 001. In Canada, the bank operates as BMO Bank of Montreal and has more than 900 branches, serving over seven million customers. In the United States, it does business as BMO Financial Group, where it has substantial operations in the Chicago area and elsewhere in the country, where it operates BMO Harris Bank. BMO Capital Markets is BMO's investment and corporate banking division, while the wealth management division is branded as BMO Nesbitt Burns. The company is ranked at number 131 on the Forbes Global 2000 list.The company has not missed a dividend payment since 1829, paying dividends consistently through major world crises such as World War I, the Great Depression, World War II, and the 2008 financial crisis; this makes the Bank of Montreal's dividend payment history one of the longest in the world.On December 12, 2021 Bank of Montreal announced the strategic acquisition of Bank of the West from BNP Paribas for US$16.3 billion.