Book I of the Chronicles of Ancient Darkness series. In this series that combines Stone Age anthropology with supernatural mythology, Torak befriends a wolf who becomes his best friend and "packmate," and they go up against supernatural bears and crazy humans alike. Thre are lots of outdoor survival scenes and tense action in these books, plus animal behavior--the way Torak and Wolf "talk" in wolfspeak is really neat. The magical elements are also fascinating, as Torak learns he has the ability to "spirit walk" in the body of animals.

See also Book 2: Spirit Walker and Book 3: Soul Eater.