Federation Day is a Federation patriotic holiday celebrated every 12 August to commemorate the signing of the Articles of the Federation and the establishment of the United Federation of Planets in 2161.

In the early 23rd century, many Federates on Earth celebrated the holiday by visiting the Starfleet War Memorial. (ENT novel: Last Full Measure)

Bajor's entry ceremony into the Federation was held on the Federation Day of 2376. However, before the parasite-controlled Shakaar Edon could sign the document, he was assassinated by Hiziki Gard. The ceremony was rescheduled and held at the end of September. (DS9 novel: Cathedral)

Federation Day was first mentioned in The Slaver Weapon.

In Star Trek Generations, the Picard Family Album contains an unseen article that gives the first Federation Day as 11 October 2161.