The mark of street art is rebellion. Born outside the traditional art system on New York subways and in Melbourne alleyways, it has become one of the most collectible and admired art genres. From Jean-Michel Basquiat and Banksy to Australia's auction-record breaking ELK, street artists are known for their sense of humour, cutting critique and dynamism. Their work can appear on walls destined to erode, hung in a gallery or as an art world prank. What remains consistent however, is that in this daringness, is always a denial of expectations.