The Moon Is a Harsh Mistress
1965, G. P. Putnam's Sons
The Moon Is a Harsh Mistress (TMiaHM) is a classic of science fiction, and one of Heinlein's better-known works -- although not among his-top five most popular. TMiaHM originally appeared as a serial in the SF magazine Worlds of If (December of 1965 through April of 1966), and then was republished as a novel. It won the Hugo Award for best science fiction novel in 1967. As noted in other reviews on this page, it is one of the primary examples of his rather extreme libertarian ideas, the origin of the phrase TANSTAAFL, and arguably the template for most moon colonies found in later science fiction.
In 2075 the moon is little more than a glorified penal colony; a place for the Earth to send criminals and force them to work to farm food for a hungry planet. However, the Loonies are not slaves by any means; they have a thriving economy and can do pretty much as they please as long as they don't cause trouble. The story follows a small band of revolutionaries trying to cause trouble.
Manuel Garcia O'Kelly-Davis, an aging computer engineer, has a secret; the central Lunar supercomputer has achieved sentience, and is bored. This works out pretty well, since 'Mike' wants company, and Mannie wants to get paid for working on Mike. Every so often Mike does something unexpected, and Mannie gets called in to fix it; he tells Mike to stop doing the unexpected thing, and they chat for a bit. Then one day Mannie attends a meeting of revolutionists that want to take back the moon for the moonies, and suddenly Mike becomes the center of a plot to throw of the shackles of Earth.
This will mean putting together a revolution, an army, a government, and, in the end, convincing the Earth that Luna deserves to be free, and does not deserve to be H-bombed. This, in turn, involves Mannie talking Mike through the intricacies of human culture, and Mike coming up with brilliant ideas. Shortly Mike and Mannie are joined by a small group of fiery, intelligent libertarians who will put their lives on the line in order to manipulate the masses into living free (or dying).
Heinlein spends quite a lot of time on various interesting ideas -- hypothetical forms of group marriage, libertarianism, the physics of low gravity and orbital mechanics, how to build the perfect rebel cell, and etc. The plot is fairly straightforward and slightly lumpy, because the true motive of the author is to introduce new ideas, not a central story. While many of these ideas (AI, mass launchers, moon colonies) are old news today, Heinlein was weird enough that a lot of his ideas are still unusual today.
TMiaHM also stands out because in addition to a lot of good science and science fiction, there is also a lot of politics, economics, and sociology. This is not uncommon in science fiction, but Heinlein was an early adopter and understood that describing a new world was much more than describing new technology. While this is apparent in many of his novels, TMiaHM may be the best single example among his works.
There is, as is usual in Heinlein works, also a downside. Heinlein takes great pleasure in being full-on sexist, having old men have sex with 15-year-olds, and just generally assuming that the point of the future is for old-fashioned men to have their most fiercely-held beliefs confirmed as generally correct and admirable. And yes, I know this was written 50 years ago; Heinlein was on the sexist side of normal even back then, not stopping at 'this is the way it is, get over it' but moving on to 'this is a good way to be, let's get way more of it!'.
That said, this is a pretty good story with a lot of interesting ideas, and Heinlein is an engaging writer. If you can get over the old-fashion with extra Heinlein on top, this is worth reading both for intrinsic entertainment value and because it is a classic of science fiction.