The chapter addresses the intersection of individual development and relationship development within the context of friendship. Friendship structures, functions, interactional processes, and outcomes change from infancy to old age according to developmental progression in physical, social, and psychological aspects of being and in conjunction with situational contexts of life. Friend relationships proceed along a continuum of intimacy from acquaintanceship or friendly relations, to casual friendship, to close friendship and reflect phases of existence from initiation to maintenance to dissolution. Based on a developmental theory, we compare friendship processes and outcomes at multiple stages of the life span. The chapter concludes with recommendations for future research on friendship from a life-span perspective.

In Western cultures, friendship is usually defined as a voluntary relationship that encompasses intimacy, equality, shared interests, and pleasurable or need-satisfying interactions. In contrast to family or even neighbor relationships, scholars view friendship as a noninstitutionalized relationship for which the norms are self-defined and fairly loose. Ordinarily, friendship is neither ritualized nor celebrated in the ways that kin ties are formalized. Although it is important to note that in other cultures friendship is more formally defined and institutionalized than in the West, and that friendships in the West actually are constrained by social structure and norms, we will not discuss friendship from that perspective here (see Blieszner & Adams, 1992, for that analysis).