Hail, Hail, the Gang's All Here is an American popular song written in 1917. The lyrics were written by D. A. Esrom (pseudonym of Theodora Morse) to a tune originally written by Arthur Sullivan for the 1879 comic opera The Pirates of Penzance. The tune is part of "With Cat-Like Tread" from Act II of Pirates and was modified by Theodore Morse from Sullivan's four-part original.
Today the chorus of the song (with revised lyrics) is perhaps more identifiable (certainly amongst Irish and Scottish communities) as being part of "The Celtic Song", sung by the fans of Glasgow Celtic in Scotland. Glen Daly recorded an "official version" of "The Celtic Song" that is commonly played at Celtic Park prior to matches.
(Original lyrics by William S. Gilbert)
The song is also referred to in Kurt Vonnegut's book, Slaughterhouse-Five:
The door was flung open from inside. Light leaped out through the door, escaped from prison at 186,000 miles per second. Out marched fifty middle-aged Englishmen. They were singing "Hail, Hail, the Gang's All Here" from the Pirates of Penzance.
The phrase "hail, hail, the gangs all here" clearly existed before the song was written; it appears, for instance, in the chorus of the 1915 song Alabama Jubilee.