Oreo is a brand of creme-filled sandwich cookie consisting of two (usually chocolate) wafers with a sweet crème filling. It was introduced by Nabisco on March 6, 1912, and through a series of corporate acquisitions, mergers and splits both Nabisco and the Oreo brand have been owned by Mondelez International since 2012. Oreo cookies are available in over one hundred countries. Many varieties of Oreo cookies have been produced, and limited-edition runs have become popular in the 21st century.

Oreo is the best-selling cookie brand in the United States, and in the 21st century it became the number one selling cookie globally, bringing in more than 500 billion sales.