"Yatta!"（やった "Hooray"） is a 2001 parody song by the fictional Japanese boy band Green Leaves (はっぱ隊 Happa-tai). The song title, yatta, is the past tense of the Japanese verb yaru ("to do"), an exclamation meaning "It's done!", "I did it!", "Ready!" or "All right!" The song was first performed as a sketch on the Japanese sketch comedy show Adventures of a Laughing Dog (笑う犬の冒険 Warau Inu no Bōken), known as Silly Go Lucky in the United States, where Happa-tai is portrayed by some of Japan's most well-known comedians. The song was written by Hideki Fujisawa, otherwise known as Dance Man (dansu man;ダンス☆マン), who has also written songs for Morning Musume and the animated TV series Sgt. Frog.
The video features its members singing and dancing exuberantly while wearing only underwear with a large green leaf on the front. The six band members' synchronized dancing and personalized poses for the camera parody the boy band craze of the early 2000s. The sketch satirizes many of the stereotypes of Japanese pop culture, including such tropes as a romantic interlude during the song's bridge that takes place on a city street filled with floating sakura blossoms.
On April 4, 2001, "Yatta!" was released under the Pony Canyon label in Japan. It surprisingly hit No. 6 in the charts and went triple-platinum in Japan within a number of weeks. While the song was intended to be humorous, some viewers outside Japan assumed it to be earnest, perhaps due to the obvious work that went into the special effects in the video. The incomprehensibility of such an elaborate video enhanced its popularity among Western audiences who could not understand the Japanese lyrics.
The song and video have since been used as a web culture in-joke on many different websites. The actors who performed as Happa-tai were brought to perform "Yatta!" in the US on Jimmy Kimmel Live!. Host Jimmy Kimmel compared himself to Ed Sullivan introducing the Beatles in their first American performance.