The foreword to Prelude to Foundation contains the chronological ordering of Asimov’s science fiction books. Asimov stated that the books of his Robot, Empire, and Foundation series “offer a kind of history of the future, which is, perhaps, not completely consistent, since I did not plan consistency, to begin with.” Asimov also noted that the books in his list “were not written in the order in which (perhaps) they should be read”.[2] In the Author’s Note, Asimov noted that there is room for a book between Robots and Empire and The Currents of Space, and that he could follow Foundation and Earth with additional volumes.