Street art has exploded: it pervades our back alleys, surrounds us at bus-stops, covers billboards, competes with advertising and generally serves as urban wallpaper in most cities. But what is street art? A far cry from mere graffiti, street art has gained some social acceptance, but it remains neither officially sanctioned like public art, nor institutionally condoned, like its more traditional artistic cousins in museums. Somewhere in between these two extremes, street art has emerged, occupying a metaphysically suspect grey area between illegal activity and bona fide art. This paper explores the nature of this emerging art form and draws out some of the differences between street art, public art and ‘mere’ graffiti.