Traditional

"When the Saints Go Marching In." often referred to as "The Saints," is a United States gospel hymn that has taken on certain aspects of folk music. The song is a slight modification (in 1927) of the similarly titled song "When the Saints are Marching In" from 1896 by Katharine Purvis (lyrics) and James Milton Black (music). Though it originated as a spiritual, today people are more likely to hear it played by a jazz band (Wikipédia).