At first glance it seems obvious where Star Wars belongs if you were to categorize it under a book genre. But if George Lucas had been trying to write a query letter, he might have run into some difficulties.
Star Wars is obviously science fiction, right? It takes place in space with plenty of battles there. We skip from one gorgeous planet to another. The technology is like what people only dream about. Hand held devices that let you communicate over distances. There was nothing like that in the 1970's when the first movie came out. Intelligent robots that are your personal servants. Robots called droids to fight your battles in lieu of actual casualties. The ability to conquer the tremendous size of the galaxy by using hyperdrive and go places instantaneously--or as good as if your hyperdrive computer hasn't been deactivated.
The movies are also populated with aliens of every shape and color. Not only have they conquered technology, but they don't seem to have a race problem. Nobody is really putting down the blue people for instance or picking on someone because they have six legs or no legs if you're a Hutt. It's an equal opportunity universe where plenty of prejudices still exist and even a smattering of slavery. I find it rather humanizing that unlike Star Trek the world here isn't perfect. There are still bad parts and nasty people. Bribery and smuggling still exist. Greed and lust for power are motivations. Money passes hands. People are still imperfect. (Compared to say Star Trek where everyone works hard because they want to? or for the good of society? I was never sure, but they don't seem worried about paychecks.)
And can we have a little aside about Princess Leia. A princess who is kickass with a blaster. A no-nonsense girl who favors serious subjects. She's in the heart of every battle, withstanding torture and riding speeders with the best of them. But she can still look like a woman as she swings across a chasm. There's a role model!
So in Star Wars the inventive and imaginative settings and use of science and technology make it obvious this is science fiction. Until we come down to the heart of the plot and the Force.
The real center of the movies is a duel between two sides of the Force--the Sith and the Jedi.
As Han Solo calls it, the Force is a hokey religion that makes use of ancient weapons. It's a power no one can see that allows certain people to manipulate it and have lightening fast reflexes, jump incredible distances, and sense things before they happen. Not to mention change the minds of the weak. In other words, it's magic.
Oh, the later movies tried to classify it as science, talking about the Midichlorian levels and microscopic beings who live in our cells for our mutual benefit. The Force pervades all life. The Midichlorians continually speak to us of the Force. It's still your dressed-up magic system however you rationalize it.
However you want to explain it, try and write a query letter about the heart of the plot of Star Wars and you have to include the Force. And what is the Force but a key aspect of the fantasy genre.
What does the story really come down to. A spunky princess, a roguish smuggler, a hero-to-be fighting the evil dictator. It has themes of honor and valor like most fantasy. It speaks to redemption. All typical themes of fantasy.
Star Wars is mix of science fiction and fantasy. A common problem that faces many writers when they try to classify their work. It's a blending of the two--a hybrid! And like any good hybrid it takes the best of both worlds and brings them together to make something greater!
So take heart everyone who has trouble classifying their manuscript. If your story has a little bit of this genre and some of that genre, you just might become the most popular story of all time!