Dublin Castle and the Department of Foreign Affairs headquarters will be lit up in blue all weekend, to mark the 70th anniversary of the United Nations.
Buildings and monuments around the world are going to be lit up including the Sydney Opera House and the Leaning Tower of Pisa.
The wave of blue is starting in New Zealand and will move across the globe as dusk falls.
The United Nations was set up on this day in 1945, and replaced the League of Nations.
