Commonwealth Day (formerly Empire Day) is the annual celebration of the Commonwealth of Nations, since 1977 often held on the first Monday of March.

The event recognises the unity and diversity of the Commonwealth, an association of 56 member states, the vast majority of which are former territories of the British Empire.

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Commonwealth countries span Africa, Asia, the Americas, Europe and the Pacific. Members are diverse – they are amongst the world’s largest, smallest, richest and poorest countries, and are home to myriad cultures and religions.

The annual celebration of the Commonwealth Day highlights how member states have become ‘free and equal’.

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While it has a certain official status, Commonwealth Day is not a public holiday in most Commonwealth countries, and there is little public awareness of it.

Early history of the day can be traced in 1898 when an "Empire Day” was introduced in schools in Ontario, Canada on the last school day before 24 May, Queen Victoria's birthday, to remind children that they formed part of the British Empire.

Later in 1904, Empire Day was introduced in the UK 'to nurture a sense of collective identity and imperial responsibility among young empire citizens'.

In schools, morning lessons were devoted to "exercises calculated to remind (the children) of their mighty heritage.”

The focus of the day was an organised and ritualistic veneration of the Union flag. Then, schoolchildren were given the afternoon off, and further events were usually held in their local community.

The day became more of a dull commemoration in the aftermath of World War I, and politically partisan as the Labour Party passed a resolution in 1926 to prevent the further celebration of Empire Day.

After World War II, the event fell into rapid decline, and Prime Minister Harold Macmillan, in 1958, announced in Parliament that the name of Empire Day would be changed to Commonwealth Day.

The main event is marked by a religious service in Westminster Abbey, normally attended by the monarch as Head of the Commonwealth along with the Commonwealth Secretary-General and Commonwealth High Commissioners in London.

Every year, there is a different theme each year for the day, focusing on an issue of importance to the Commonwealth. The theme for this year is ‘Forging a sustainable and peaceful common future’.

It will focus on the active commitment of member states to support peace, prosperity and sustainability, especially through climate action.

In the UK, this years’ service will be the first delivered by King Charles III’ as King and Head of the Commonwealth.