At least 8.5 million soldiers are believed to have perished in the 1914-18 war.
France, where the majority of Western Front fighting took place, is taking a leading role in the preparations.
Senior officials from countries including the US, Britain and Australia were gathering today under the Arc de Triomphe for a ceremonial re-lighting of the eternal flame that marks the tomb of France's unknown soldier.
Meetings continue tomorrow under the golden dome of the 17th-century Invalides monument, hosted by France's veterans' affairs minister, Kader Arif.
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The Australian minister for veterans' affairs, Michael Ronaldson, said it was important that participants "start defining where we all want each other to be and when."
"We'll be talking about those key events that everyone wants to commemorate. We'll be talking about what the hopes and aspirations of each country are" regarding the different commemoration events, Ronaldson told The Associated Press.
Each nation has their own significant wartime events, Australia and New Zealand, for example put particular emphasis on the 1915 battle of Gallipoli, where their joint force was defeated by the Ottoman Turks.
"I think that will make it work as opposed to detract from it."
Ronaldson, whose grandfather fought on the Western Front, also visited the Australian National Memorial in Villers-Bretonneux, where the names of over 10,000 Australians who died in France during World War I and who have no known grave are inscribed.
"Those visits for all Australians are always deeply emotional and it was the same for me yesterday," Ronaldson said.