"Today is Gonna Be a Great Day" is the full version of the series' theme song. It is performed by the band Bowling For Soup. The song is composed in a fast, loud rock styling, but was originally written as a slow song with a light chorus, based on classic Disney songs. Many stanzas in the song are at least closely resembling actual adventures and inventions Phineas and Ferb take part in throughout the series, while others are merely interesting things the boys could possibly do. The song first appeared in its entirety in the episode "Phineas and Ferb's Quantum Boogaloo," and then was released as part of the official series soundtrack.