I have moved this over to General Book Discussions, as Book Search is generally for a specific title.
On the query posted... you might want to look at this site concerning Heinlein:
Heinlein Society - Official Robert Anson Heinlein Estate Endorsed Website
It will give several suggestions on resources where he is concerned. Personally, despite the official Heinlein site's reservations, I found Leon Stover's book on Heinlein (part of the Twayne's United States Authors Series) to be quite interesting, while Panshin's
Heinlein in Dimension I found to be somewhat less useful, though I would still recommend it as an example of what Heinlein criticism was for a very long time (and, in many areas, it is still like this). Joseph Olander and Harry Martin Greenberg's anthology of critical essays on Heinlein is... very disappointing, and often simply bad criticism. However, Jack Williamson's essay on Heinlein's juveniles is the best I've come across on that topic, and well worth looking up.
General histories of sf are numerous, as are more general sf reference books. Among those I would recommend would be Brian W. Aldiss'
Trillion Year Spree and Lester del Rey's
The World of Science Fiction, 1926-1976: The History of a Subculture;
The Encyclopedia of Science Fiction, by John Clute and Peter Nicholls; and, if you can find it, Harry Warner Jr.'s
All Our Yesterdays: An Informal History of Science Fiction Fandom in the Forties (a period when Heinlein had more of a tie to fandom than he would have later in his career, as I recall). I would also suggest getting a copy of Heinlein's
Grumbles from the Grave, which is a collection of his letters, often discussing various aspects of his career.
You might also want to look at the references given here:
History of science fiction - Wikipedia, the free encyclopedia