The coat of arms of Canada, also known as the Royal Coat of Arms of Canada or, formally, as the Arms of His Majesty The King in Right of Canada, is the arms of dominion of the Canadian monarch and, thus, also the official coat of arms of Canada. In use since 1921, it is closely modelled after the royal coat of arms of the United Kingdom, with French and distinctive Canadian elements replacing or added to those derived from the British version.

The maple leaves in the shield, blazoned "proper" (i.e., in natural colour), were originally drawn vert (green), but were redrawn gules (red) in 1957 and a circlet of the Order of Canada was added to the arms for limited use in 1987. The arms are registered with the Canadian Heraldic Authority and protected under Crown copyright; they are used to signify national sovereignty and the federal government uses the arms to represent the state under the Federal Identity Program. Elements of the coat of arms are also used in other designs, with the shield being used in the various royal standards belonging to members of the royal family and the crest of the arms serving as the focal point of the governor general's flag.

Prior to Confederation in 1867, the royal coat of arms of the United Kingdom served in Canada as the symbol of royal authority. Arms had not been granted to any of the colonies in British North America, apart from 17th century grants to Nova Scotia and Newfoundland. Arms were then granted by royal warrant, on 26 May 1868, to Ontario, Quebec, Nova Scotia, and New Brunswick. (That Nova Scotia had previously been granted arms was forgotten and it took until 1929 for the historic arms granted in the 17th century to be reinstated.) In that warrant, Queen Victoria authorized the four arms of the first provinces to be quartered for use on the Great Seal of Canada. While this was not done for the first Great Seal, it was through that reference that the arrangement became the de facto arms for Canada until 1921, which were used on the first Red Ensign carried by Canadian troops at Vimy Ridge in 1917.^{[citation needed]}

As more provinces and territories joined Canada, the original four arms were marshalled with the arms of the new members of Confederation, eventually resulting in a shield with nine quarterings. This occurred by way of popular and even Canadian governmental usage; flag-makers took to using the complex shield on Canadian Red Ensigns. None of those shields, besides the original four-segment version of 1868, were ever official in any sense, nor were any of these shields a national "coat of arms", as they had never been approved by the monarch.

Heraldists considered nine quarterings on a shield as too convoluted for a national symbol and, by 1915, a push had begun to design a new coat of arms for Canada. A committee, which included Dominion Archivist Arthur Doughty, was formed in 1919 to pursue the issue, eventually agreeing that the elements of the new arms would reference the royal arms of England, Ireland, Scotland, and France, with maple leaves representing Canada, though there was at the time no consensus on how the leaves were to be used. A 1917 proposal by Edward Marion Chadwick (who had designed the crest, supporters, and motto of the coat of arms of Ontario) sparked a discussion about featuring First Nations figures as supporters. Though Chadwick had depicted the clothing and regalia accurately, Joseph Pope rejected the idea, stating, "I myself do not see any necessity for commemorating the Indians at all."

The arms' design was settled by the following year and the committee conferred with the College of Arms in London, only to face resistance to the use of the UK's royal arms from the Garter King of Arms, as well as concern over whether the inclusion of the fleurs-de-lis would imply Canada claimed sovereignty over France. The Canadian Commissioner-General in Paris discreetly confirmed with French officials that the coat of arms would not spark a diplomatic spat. A counter-proposal from the college added the flags to the supporters and a crown to the lion, as in the British arms, and placed the three fleurs-de-lis between two green maple leaves in the fifth charge on the shield, below the four charges of the arms of the UK.

After some manoeuvring, including the personal intervention of Winston Churchill, the new arms of Canada were eventually formally requested by an order-in-council on 21 April 1921 and adopted on 21 November of the same year, by proclamation of King George V, as the Arms or Ensigns Armorial of the Dominion of Canada;. the committee records were preserved with Library and Archives Canada. The new layout closely reflected the arms of the United Kingdom, with the addition of maple leaves in the base and the reference to the French royal arms in the fourth quarter.

Eugène Fiset, the Deputy Minister of Defence, claimed in 1918 that the design of the arms would determine the national colours of Canada and an unnamed member of the committee stated, "the colours of the shield will become the national colours of the Dominion [...] the red maple leaf has been used in service flags to denote men who have sacrificed their lives for the country [...] The case for white is that it contains an allusion to snow, which is characteristic of our climate and our landscape in certain seasons." In the 1940s, military historian Archer Fortescue Duguid suggested King George V had chosen red and white as Canada's official colours because those were the colours in the wreath and mantling on the arms. However, Forrest Pass, a curator at Library and Archives Canada, determined there is no record of either the King or the committee giving much importance to the mantling and the royal proclamation of the coat of arms makes no mention of national colours, specifically.