The Bonnie Lass o' Fyvie is a Scottish folk song about a thwarted romance between a soldier and a girl. Like many folk songs, the authorship is unattributed, there is no strict version of the lyrics, and it is often referred to by its opening line There once was a troop o' Irish dragoons. The song is also known by a variety of other names, the most common of them being "Peggy-O."