"Happy Days Are Here Again" is a song copyrighted in 1929 by Milton Ager (music) and Jack Yellen (lyrics). The song was recorded by Leo Reisman and His Orchestra, with Lou Levin, vocal (November 1929), and was used in the 1930 film Chasing Rainbows. The lyrics suggest optimism and buoyancy: :The skies above are clear again, :Happy days are here again. :There's no one who can doubt it now. :Happy days are here again. :There'll be no more from now on! Matthew Greenwald characterized it, "A true saloon standard, Happy Days Are Here Again is a Tin Pan Alley standard, and had been sung by virtually every interpreter since the 1940s. In a way, it's the pop version of Auld Lang Syne."

The song is #47 on the Recording Industry Association of America's list of "Songs of the Century".

"Happy Days Are Here Again" became closely associated with the 1932 campaign of Franklin Delano Roosevelt for the U.S. presidency, and was prominent at the Democratic Party Convention of that year. Since that time the song has been associated with the Democratic Party, and remains a sentimental favorite for Democrats.

One of the most influential recordings of the song was made 33 years after its first recording; this was Barbra Streisand's version in her 1963 album debut The Barbra Streisand Album. She also sang this song on The Judy Garland Show, in a medley with Judy Garland's Get Happy. While the song is traditionally sung at a brisk pace, her recording is notable for how slowly and expressively she sang it. By 2006, 76 commercially released albums included versions of the song.

Television and nightclub comedian Rip Taylor has used "Happy Days Are Here Again" for years as his theme song. He always makes his entrance, with bag of confetti in hand, to the strains of his song.

In 1930 the Comedian Harmonists recorded their popular German adaptation, Wochenend und Sonnenschein.