This chapter provides an overview of the family as the basic social unit of beaver society. A beaver family consists of the parents, the young of the year, and yearlings. Two-year-olds may or may not be present; they usually leave or are expelled when or before a new litter is born. On average, there are two kits of the year and two yearlings, so that a typical family on a reasonably good site numbers about six members, provided there is no trapping or other disturbance to the colony. This chapter discusses beaver family size and composition, lodge use and site defense, home range, behavior inside the lodge, and parenting. It shows that beavers rely on chemical secretions to recognize family members, which is important in coordination of social behavior, separation of roles, and defense against invading beavers. It also considers the division of labor in the beaver colony.