My Side of the Mountain is the 1st book in the Mountain Series.

Every kid thinks about running away at one point or another; few get farther than the end of the block. Young Sam Gribley gets to the end of the block and keeps going - all the way to the Catskill Mountains of upstate New York. There he sets up house in a huge hollowed-out tree, with a falcon and a weasel for companions and his wits as his tool for survival. In a spellbinding, touching, funny account, Sam learns to live off the land, and grows up a little in the process. Blizzards, hunters, loneliness, and fear all battle to drive Sam back to city life. But his desire for freedom, independence, and adventure is stronger. No reader will be immune to the compulsion to go right out and start whittling fishhooks and befriending raccoons.