Demography may not be destiny, but it surely sets some important constraints on what is feasible and desirable in the broader social, economic, and political world. The present research program aims to explore the manner in which demographic change - in particular, changes in the age distribution of a group, organization, or entire society - conditions social interactions. A theoretical framework will be designed that enables an appreciation of how demographic changes - both expected and unanticipated - filter through the broader society and political economy. These changes potentially perturb established inter-temporal relationships, sometimes enabling new social arrangements to be sustained, other times reducing the feasible set. Of special theoretical interest is the effect of demographic shocks on inter-temporal relationships termed seniority arrangements. One specific aim of this research program, then, is to develop a theoretical framework that gives prominence to (organizational and calendar) age, allowing for a rather general conception of "aging" and a more dynamic assessment of the stability of age-based arrangements. In short, this project highlights the ways in which the age distribution of a group or population affects seniority relationships within its ranks. Because the theoretical analysis is formulated in a general fashion to accommodate a broad range of phenomena, it provides a basis for empirical inquiry in a number of interesting settings. This is the second 3pecific aim of the research program. The examination of three empirical settings - seniority arrangements in legislatures, age-grading in tribal societies, and pension policies in industrial democracies -will provide especially instructive contexts in which to elucidate theoretical relationships about age, seniority, and demographic perturbations.