Many people tend to think of science fiction as little more than the trappings of pop culture phenomena like Star Wars and Star Trek. You know the stuff we're talking about: robots, lasers, green-skinned vixens, bug-eyed aliens, spaceships traveling at warp speed, and an evil space empire or two thrown in for good measure.
By those standards, The Moon is a Harsh Mistress might not seem like much in the way of science fiction. The story only takes place on the Moon after all, and humanity marked that off its to-do list back in 1969.
But Heinlein's novel is science fiction in more ways than just hi-tech trappings. By taking us to the Moon, we're forced to look at life on Earth differently—to reconsider both our own world and our role in the universe. In other words, it isn't just robots and alien civilizations and lunar revolutions that make science fiction tick.
So the next question must be: How does The Moon Is a Harsh Mistress make us think about our own world differently? For that, we must consider its other genres, philosophical literature and dystopian literature.
At the beginning of the novel, the citizens of Luna are under the dystopian rule of the Authority. It's not the socially repressive of famed dystopian novels 1984 or Brave New World. Instead, it's more of an economic dystopia—the people of Luna are in forced to do business with the Authority, a governmental entity that rigs the economic game to its advantage. As Professor de la Paz puts it, "It strikes at the most basic human right, the right to bargain in a free marketplace" (2.89).
The revolution that follows is one to replace that dystopia with what the revolutionaries see as the answer: an anarcho-libertarian philosophy. The novel uses the estranged setting of the Moon and the story of galactic rebellion to explore what it sees as the values of this philosophy and a society built within its framework. And as such, the genres of science fiction, dystopian literature, and philosophical literature all come together to create the themes of the novel.