Picasso was, it can be agreed, the quintessential avant-garde artist. His radical interrogation of painting’s established conventions in the artistic “ism” that he pioneered, Cubism, became the lingua franca for the artistic avant-garde for much of the tewentieth century. But what, specifically, did it mean to be ‘avant-garde’ in that pre-First World War decade when artistic experimentalism was becoming professionalized, and yet was in conflict with prevailing professional artistic standards? What did experimentalism in painting signify at a time of new visual technologies and a flourishing popular culture? How “professional” was Picasso? This paper offers some answers to these questions.