This is the first book in the Song of the Lioness Quartet, and despite the rather childish writing style at the beginning, it's a great book. Not my favorite of the series, but one of the better ones.
The story starts off with Alanna and Thom of Trebond, twins who are heading off to school for the first time. Well, they plan to send Alanna to a convent and Thom to the palace for training as a knight, but Alanna has other ideas. She goes to the palace instead, disguised as "Alan," and her brother heads off to the Monastery to be trained as a Mage.
She soon discovers that training to be a page will not be easy, although she does make many friends in her quest, including the Prince of Tortall, Jonathan, and George (!), King of the Rogue in Corus. And enemies...well, you have to read it to find out. It's one of my favorite books and a lot of people have their lives changed just by reading it.
Purple Flame/the Library/the Main Page