Future History or "Heinlein Timeline" is a 20-book series with 25 released primary works first released in 1940 with contributions by Robert A. Heinlein, H.B. Fyfe, Ross Rocklynne, Leigh Brackett, Willy Ley, Harl Vincent, R.S. Richardson, Norman L. Knight, L. Ron Hubbard, and Pietro Cheli.