Phineas and Ferb the Movie: Across the 2nd Dimension is a 2011 American animated musical action-adventure comedy television film based on the animated TV series Phineas and Ferb. The film premiered on Disney Channel on August 5, 2011, in the United States. It was first announced by Jeff "Swampy" Marsh during a January 2010 interview with the Daily Telegraph. The events of the film take place during the third season of Phineas and Ferb. It is the first feature-length film of the Phineas and Ferb series, and the third animated Disney Channel Original Movie, following Kim Possible Movie: So the Drama and The Proud Family Movie.

The film's premiere averaged 7.6 million viewers, making it one of the highest-rated animated programs on cable in more than three years. It later gained over 3 million viewers to become the second most watched animated basic cable telecast ever among kids 6–11 and teens 9–14, and cable's fifth highest viewership movie ever in total viewers. A standalone sequel, Phineas and Ferb the Movie: Candace Against the Universe, was released on August 28, 2020, on Disney+.