The Souls of Black Folk is a collection of essays that include history, folklore, sociology, and even autobiography to describe and illustrate the central position of African-Americans within American society as a whole. In the very famous introduction to the book, Du Bois argues that race is a crucial aspect of the American experience:
...herein lie buried many things which if read with patience may show the strange meaning of being black here in the dawning of the twentieth century. This meaning is not without interest to you, gentle reader; for the problem of the twentieth century is the problem of the color-line.
The remainder of the book is devoted to illustrating the various aspects of the "problem of the color-line" and its implications for an African-American identity. He argues that African-Americans were "dual people," not regarded as fully American by the white mainstream, at least not across the country. Du Bois himself was a renowned academic in the North and indeed around the world, but could not even use the same water fountain as a white man in the South. Much of the book revolves around these contradictions, which together both result from and comprise the divide between whites and blacks, in other words, the "color line."