According to Phil Lynott biographer Mark Putterford, the group composition "Emerald" was "the last word on the author's burning fascination with Irish history, a blood-curdling clash of steel and morality embedded upon a spectacular Gaelic guitar riff". Lyricist Lynott, the band's leader, front man and principal writer had a lifelong fascination with the history and legends of the Emerald Isle, in spite of being not only half black but technically an Englishman. The song is certainly one of his and their finer efforts with the trademark Lizzy duel guitar lead.

"Emerald" was released as the B Side of "The Boys Are Back In Town" on the Vertigo label in April 1976. >>

The song originated from a riff that Phil Lynott had. Guitarist Scott Gorham told us: "It's got the real sort of Irish-y feel in it. Brian Robertson and I, we came up with the harmony guitars in there. But the main riff came straight out of Phil. It's a song about ancient times in ancient Ireland, talking about the warring clans and all that.

It was the first time that Brian Robertson and I did the bounce off lead guitar thing where he starts," he continued. "I start, he starts, I start... the back and forth. That's the first time we actually got that one together. It felt so good and it felt so right, so we then started to try that out on a couple of other songs. That was kind of a launching pad for that style of writing between the two guitarists."