The present publication is the first complete translation of "Die Pflanzenwelt von West-Australien, südlich des Wendekreises" by Diels. The translation makes this major work on the ecology, vegetation and biogeography of Western Australian plants now accessible to a wider, english speaking community. More than 100 years after the German edition of Diel‘s seminal work (Diels, 2006) is still remaining actual even if taxonomic classifications and ecological data have changed. The translation uses the original taxonomy and data published by Diels. Diels work presents the results of an expedition during 1901–1902. His study focuses on the inter-relationship of plant life in Western Australia. The own peculiar flora and fauna of the island continent Australia which was for a long time isolated from the rest of the world and their inhabitants is Diels main concern. His publication gives a short introduction in the vegetation of the whole Australian Continent, history and literature up to 1905, the geographic setting in Western Australia and a detailed overview and classification of the vegetation in the Southwest Province and the Eremaean Province. Diels study is closed by the presentation of the flora of extra-tropical Western Australia and its classification. The translation of Diel‘s study is added with an taxonomic update. To illustrate the vegetation changes since Diels‘ time, as many as possible of the original photographic sites that could be identified were revisited and new photographs were made (Lamont & Grieve, 1984).