This contribution reconstructs a particular period in the history of ecological thought in
Germany from the end of the 19th century to Nationalsocialism. Indeed, some key concepts
used largely in ecological thought are formulated at this time: Oecologie, Umwelt, milieu and
Lebensraum. The reconstruction of the meaning, use of these pivotal concepts, as the
consideration of the political and intellectual milieus where they were developed are the
object of this contribution, that considers their further development and appropriation
during the phase of Nationalsocialism. In particular the changing meaning of the ideas of
Oecologie, Umwelt, Oecumene and Lebensraum will be explored from the works by Ernst
Haeckel and Friedrich Ratzel, to the Nationalsocialist ecological movements, supported by
Rudolf Hess and Richard W. Darré
