Future History or "Heinlein Timeline"

Future History or "Heinlein Timeline" is a 20-book series with 20 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, and L. Ron Hubbard.