Volturi, Jacob v. Edward, James v. Edward. Who decides what makes someone good and someone else bad? Are there different levels of evil? Then there is the theme of love. The unrequited love that Jacob has for Bella. The forbidden love between Bella and Edward. Many of the themes in theTwilight Saga parallel those found in Romeo and Juliet. Meyers often makes references to the Shakespeare play in the first and second novels. I'm sure that this was not done by accident. Another theme you may want to explore is "Choice". Should Bella choose Edward or Jacob? Should she stay human or become a vampire? Should she keep her baby or not? In New Moon, Edward makes a choice to leave Bella and then chooses to come back to her. The possibilities are endless. Good luck!

I think the most important theme of the Twilight series (especially in the early books) is the ethical choice that the Cullens make. They choose to deny their own nature in order to be moral people. There is also a lot of talk about the soul, and the question of whether vampires have souls (Edward doesn't think so, Carlisle believes they do).

In response to Jlcannad, I agree that the last book is very different from the first three. Part of me was happy that it everyone gets to live happily ever after and be fulfilled, but another part of me doesn't quite believe that everything would get wrapped up so nicely like that. I think there are a lot of conflicting ideas regarding the last book out there, but if Meyer had killed off Bella, think of how many angry fans there would be!

I agree that the Mormon concept of "agency" or choice is foremost in the first three books.  Does Edward choose temptation or protecting Bella.  Does Bella choose her vampire or her werewolf? Is it better to have true love or children?  An education or immortal life?  Freedom or love?  There's always choice in the books, which is why the last book is just so odd.  Jacob's choice is ripped from him when he imprints on Bella's child.  Bella's need to choose is ripped away when she gets the vampire and a child.  Her father... well, that thread just weirdly vanishes.  I truly don't think the last book has anything to do with the first three.

Based on my reading of the books thus far, interviews of Meyers, and reviews of her series, the most important theme of her books deals with the choices we make in life. In one interview, Meyers says, "It doesn't matter where you're stuck in life or what you think you have to do; you can always choose something else. There's always a different path." This is seen in Edward's willingness to resist the temptation to bite Bella's neck, even though his desire to do so is great. Her characters choose to abstain from wrongdoing and show great self-restraint. It is the moral strength of her characters that draw many people to the books.

A statement of theme means that you are being asked to state (write) what a central theme of a piece of literature is.  Theme can be defined as a main idea or underlying meaning of a literary work.  Generally a statement of theme needs to be followed up with supporting evidence.  It's not good form to state that a theme is present without providing evidence to support that claim.    

One theme that is present in Twilight (and the rest of the series) is love and desire.  Bella and Edward are hopelessly in love with each other.  Jacob is in love with Bella.  The rest of the Cullen couples are in love with each other.  The book is full of teenage love and desire.  

I think another theme is the theme of mortality and immortality.  That theme is closely tied with the theme of choices as well.  Bella is mortal, and the Cullens are immortal.  Bella has a choice throughout the series to become like the Cullens, and a great deal of time is spent discussing the positives and negatives of such a choice.