To create Guitar Picasso made a radical leap from the sculptural tradition of modeling (carving or molding) to a new technique of assemblage. He created a first version of Guitar from cardboard in 1912, then later remade the work in sheet metal; the modern ordinariness of both of these materials is very different from traditional sculptural materials such as bronze, wood, and marble. The planes of the sheet-metal construction engage in a play of substance and void in which volume is suggested, not depicted. In a dramatic demonstration of the flexible way visual forms can be read in context, the guitar's sound hole, which normally recedes from the instrument's smooth surface, here projects outward into space.

Early visitors to Picasso's studio were bewildered by this work: "What is that?" they asked, according to the poet Andre Salmon: "Does that rest on a pedestal? Does that hang on the wall? Is it a painting or sculpture?" Apparently, Picasso responded, "It's nothing, it's 'la guitare!'" For Salmon, one of Picasso's closest friends during the Cubist years, the effect was of radical importance: "We were delivered from painting and sculpture, liberated from the imbecilic tyranny of genres." With its center open to space, Picasso's Guitar was a radical breakthrough.