People in the US and four other countries including China and Saudi Arabia have been celebrating the centenary of the Oreo cookie.
Flash mobs in seven US cities sang "Happy Birthday!" to the famous comfort food: a white filling (or cream) sandwiched between two black biscuits.
The first Oreos were baked at the Nabisco factory in New York in 1912.
They are now sold around the world, bringing Kraft Foods - which owns Nabisco - $2bn (£1.3bn) annually.
"It's the best-selling cookie in the world," said John Ghingo, senior director for Oreo Global at Kraft.
"The simple act of enjoying an Oreo cookie and glass of milk continues to speak to a universal, human truth: inside all of us... there's a kid that deserves to be set free every once in a while," Mr Ghingo said.
He added that the name Oreo remained mystery even today, but one theory suggested that the two uses of "O" in the word represented the cookies and the "re" in the middle stood for the cream.
To mark the milestone, the company released a limited edition of "Birthday Cake" Oreo.
On Tuesday, celebrations were also held in China, Indonesia, Saudi Arabia and Venezuela.