Book excerpt: This selection of essays by a prominent art historian, critic and curator of modern art examines the art and artists of the twentieth century who have operated outside the established art world. In a lucid and accessible style, Peter Selz explores modern art as it is reflected, and has had an impact on, the tremendous transformations of politics and culture, both in the United States and in Europe. An authoritative overview of a neglected phenomenon, his essays explore the complex relationship between art at the periphery and art at the putative center, and how marginal art has affected that of the mainstream.