President Mary McAleese is to lead a wreath-laying ceremony outside the GPO in Dublin later to mark the 95th anniversary of the 1916 Easter Rising.
Three hundred members of the Defence Forces from the army, air corps and naval services will also take part in today's event.
At noon today, the Irish flag will be lowered outside the GPO, which served during the Rising as the headquarters of Padraig Pearse, commander of the Volunteers.
Taoiseach Enda Kenny and Defence Minister Alan Shatter will be among those attending the commemoration, along with relatives of those who fought in 1916.
The 1916 Proclamation will be read by a naval officer, and a minute's silence will be observed.
The half-hour ceremony will end with a flypast by the Air Corps.
Traffic restrictions are already in place near O'Connell Street ahead of the event.