Why aren't Rosalie and Jasper surnamed Cullen? I can't understand why they are Hale and not Cullen.
Everyone believes that all the Cullen "kids" are adopted. Alice, Edward, and Emmett go by the last name "Cullen" while Rosalie and Jasper go by "Hale". I agree with Zoe that it makes sense that, since Alice and Jasper are obviously in a relationship with each other and Rosalie and Emmett are in a relationship together, it would bring more attention to the family if it was suggested that they were dating their siblings even if those siblings were adopted as well. Additionally, it sort of makes sense to have Jasper and Rosalie share a name and pretend to be real siblings since they look similar (both have blond hair).
Interestingly, Jasper's real last name isn't Hale anyway...it's Whitlock.