The President and the Taoiseach are to attend ceremonies in Dublin at noon tomorrow to mark the 90th anniversary of the Battle of the Somme.
Thousands of Irishmen were among the half a million soldiers who died in the battle.
The ceremony in Dublin to mark the Battle of the Somme will be held at the National War Memorial Park at Islandbridge.
Over three and a half thousand Irishmen - from North and South died in the major 4-month offensive in North Eastern France, which began on July 1, 1916.
800 guests have been invited to the ceremony; it is also open to the general public.
President McAleese and eight ambassadors will lay wreaths at the Cenotaph, and members of the British Legion will present books bearing the names of the dead.
About 200 members of the Defence Forces are taking part - the first large-scale involvement of Irish troops in ceremonies to mark the First World War.
Live coverage of the ceremonies start on RTÉ One television at 11.30am.