According to a 1986 interview with The Edge:
MUSICIAN: And who were the influences on you as a guitarist?
EDGE:: I was very influenced by Tom Verlaine- not stylistically, but in terms of general approach and tearing up the rule-book. I also loved Patti Smith: her guitar-playing was competent and not particularly exceptional, but it was perfect for her band. These influences never became very evident; they were always more of an inspiration, catalysts in the formation of my own style.
MUSICIAN: How would you characterize your own way of playing?
EDGE:: Style is a very complex thing. There are various guitar sounds that interest me, and one of them is a melodic, linear way of playing, that has a kind of cutting clarity. I realized quite early on that a harmonic, let's say, can be so pure and finely-focused that it has the incredible ability to pierce through its environment of sound, just like lightning. I've always wanted to be able to do that. But I would pick out many different aspects of my playing. Perhaps most important of all is the Irish influence on my use of drone strings, which was something I started to do quite instinctively, before I could afford a bank of expensive effects. In the early years I used quite clean sounds, generally playing higher strings, and plucking them with a pick, but playing the melody against a drone.
MUSICIAN: How do you do that?
EDGE:: It sounds very complex, but really it's just a rhythmic device. The idea of playing over a drone is very Irish, and as far as I know has no roots at all in rock 'n' roll. Another of my traits, which is similar, is the use of echo in a rhythmic way.