The term avant-garde is no longer considered de rigueur as a description of boundary-testing artists, but that does not mean that an artistic underground has ceased to exist.
However, finding out about those artists who test the boundaries of their art is not as easy as stepping into your local book store or record shop.
But help is at hand. As part of Today guest editor Zadie Smith's programme, the author Hari Kunzru has put together a starter kit to those artists in the artistic vanguard.
By definition, the underground is - underground. So there's no overview, no definitive guide. This is a partial, ill-informed, cobbled together list of stuff, being made mostly in Britain, which is in some way difficult, experimental, marginal, odd, or otherwise unlikely to be available on your local high street.
There's the post-language poetry scene, around Keston Sutherland et. al in Sussex.