“Wouldn’t It Be Nice” is a song written by Brian Wilson, Tony Asher, and Mike Love for American rock band the Beach Boys. It was released as the opening track on their 1966 album Pet Sounds.
Like other tracks for Pet Sounds, Wilson constructed the song’s symphonic Wall of Sound arrangement using a variety of instruments not normally associated with popular music of its time, including accordions and a detuned twelve-string guitar.
The music contains classical music devices that are unusual for a rock song, such as bitonality and ritardando. After recording the instrumental track, the Beach Boys overdubbed their voices to Wilson’s exact specifications. [source]