Over the last two decades, significant advances have been made in the social sciences that bear directly on the theory of family development. Among these are: an increased awareness that the «MDUL»family«MDNM» can be discussed on several different levels and each of these levels of analysis requires separate theoretical and conceptual treatment; the role of mathematical models in theory construction; and a refinement and application of dynamic modeling. Incorporating these advances, this groundbreaking work provides a reconceptualization and expansion of the most popular theoretical framework in the study of families. It is about the myriad ways in which families traverse their life course. But, first and foremost, the volume is intended as a statement of the theory of family development.