Coming to prominence during the tropical booms of the late nineteenth and early twentieth centuries, the Putumayo has long been a site of mass immigration and exile, of subjugation and insurgency, and of violence. By way of a study of literature of and on the Putumayo by Latin American as well as US and European writers, Colombia’s Forgotten Frontier explores the history and enduring significance of this Amazonian border zone, which has been visited both physically and imaginatively by figures such as Roger Casement, José Eustasio Rivera, and William Burroughs. Travel writing, testimony, diaries, letters, journalism, oral history, songs, photographs, and ‘pulp’ fiction are all considered alongside more conventional forms such as the novel. Whilst geographically peripheral, the Putumayo has played a central role in Colombia and beyond, both historically and, crucial to this study, culturally, producing a literature of extreme experience, marginality, and conflict.