Shiver (Book #1 in the The Wolves of Mercy Falls Series) By Maggie Stiefvater

From a dazzlingly talented young writer, a haunting and original supernatural romance in the vein of TWILIGHT. For years, Grace has watched the wolves in the woods behind her house. One yellow-eyed wolf--her wolf--is a chilling presence she can't seem to live without. Meanwhile, Sam has lived two lives: In winter, the frozen woods, the protection of the pack, and the silent company of a fearless girl. In summer, a few precious months of being human...until the cold makes him shift back again. Now, Grace meets a yellow-eyed boy whose familiarity takes her breath away. It's her wolf. It has to be. But as winter nears, Sam must fight to stay human--or risk losing himself, and Grace, forever. Excellent condition