Like all complex living systems, a family, during its life course, proceeds through predictable stages of development. Yet every family is different, its uniqueness defined and continually redefined by an open-ended array of structural, biological, and sociocultural variables. And, as with all living things, a family s continued well-being depends upon its ability to adapt to changes arising from both within the family system and without.

First postulated in the 1940s, these basic ideas constitute the conceptual core of modern family development theory. From them has blossomed an...