A series of events are being held to mark 100 years since Britain declared war on August 4, 1914, attended by members of the Royal Family and senior politicians from Britain, Ireland, Germany, Belgium and the Commonwealth.
The events are part of a commemoration spanning the four-year centenary of the Great War, with events due to take place in the UK and Belgium.
On Monday August 4, there will be events at Glasgow Cathedral, St Symphorien cemetery in Mons, Belgium, and at London's Westminster Abbey.
Setting out details of services of remembrance in London and Glasgow and a commemorative event in Belgium, Culture Secretary Sajid Javid said: "A hundred years on, the sheer scale and sacrifice of the First World War demand remembrance.
"Breaking with tradition, we are marking the start as well as the end of the conflict so that the anniversaries of the war will improve our understanding of its causes, conduct and consequences."
On August 4, a service for the Commonwealth will be held at Glasgow Cathedral, attended by the Prince of Wales.
Led by Glasgow Cathedral minister Dr Laurence Whitley and organised with Glasgow City Council, it will honour the present-day Commonwealth's contribution to the war.
The service, which will be shown live in George Square, will be followed by a procession to the Cenotaph in the square for a wreath-laying service and march-past.
Later that day, the Duke and Duchess of Cambridge and Prince Harry will attend an evening ceremony at the Commonwealth War Graves Commission's cemetery at St Symphorien, where the first and last British soldiers who died on the Western Front are now buried.
The land at St Symphorien was given to the German army by a Belgian landowner on the condition that the cemetery provide a suitable resting place for the dead from both sides of the conflict, and that all were buried with due respect.
The first and last British, and the last Commonwealth, soldiers to die on the Western Front are buried there along with the first recipient of the Victoria Cross.
The event for around 500 invited guests will include readings, music and poetry capturing the history of the site and the ceremony will acknowledge the British, Irish, Commonwealth and German war dead that lie there in almost equal numbers.
The service, narrated by historian Dan Snow, will be screened live in Mons town square and will include a recording of a unique collaboration between the London Symphony Orchestra and the Berlin Philharmonic Orchestra playing together; readings of soldiers' letters and reflections; a performance by a children's choir conducted by Gareth Malone; and a new commission from composer Howard Goodall.
At 10pm on the same day, a service of Solemn Commemoration at Westminster Abbey will feature the gradual extinguishing of candles, with an oil lamp being extinguished at the Tomb of the Unknown Soldier at 11pm, the exact time Britain joined the First World War.
The service, conducted by the Very Reverend Dr John Hall, Dean of Westminster, will include music by Elgar, Parry, Walton and Purcell with readings from the Bible, letters sent home from the front, the poem 1914 by Wilfred Owen, Birdsong read by its author Sebastian Faulks and works by Rose Macaulay and Isaac Rosenberg.
It will also feature music by JS Bach and a prayer spoken in German. As the fourth candle is extinguished, The Lark Ascending by Ralph Vaughan Williams, arranged for violin and organ, will be played.
The final light will be extinguished by the Duchess of Cornwall.
Alongside this, similar services will be held in Anglican churches around the UK, including St Anne's Cathedral in Belfast and Llandaff Cathedral in Cardiff, with other churches and faiths planning acts of prayer.
And during the same hour, places of worship, other public buildings, workplaces and private homes will take part in Lights Out, a Government-backed project to see lights switched off across the country for an hour from 10pm, echoing the reported comment by then foreign secretary Sir Edward Grey about the lamps going out across Europe.
It is hoped that every household will join in the project, leaving a single light or candle burning as a symbol of hope in the darkness.