The fifteenth season of the American television sitcom series It's Always Sunny in Philadelphia premiered on FXX on December 1 and concluded on December 22, 2021.

This season had next day availability on FX on Hulu and FXNOW.

The season consists of eight episodes and makes the series the longest-running live-action scripted comedy series in American television history, surpassing The Adventures of Ozzie and Harriet.

[1] The series was renewed for a fifteenth season in May 2020, making it the longest-running live-action comedy series in American television history, replacing The Adventures of Ozzie and Harriet, which ran for 14 seasons between 1952 and 1966.

[2] On April 9, 2020, Rob McElhenney announced that writing had begun for season 15.