Hierarchy is such a defining and pervasive feature of organizations that its forms and basic functions are often taken for granted in organizational research. In this review, we revisit some basic psychological and sociological elements of hierarchy and argue that status and power are two important yet distinct bases of hierarchical differentiation. We first define power and status and distinguish our definitions from previous conceptualizations. We then integrate a number of different literatures to explain why status and power hierarchies tend to be self-reinforcing. Power, related to one's control over valued resources, transforms individual psychology such that the powerful think and act in ways that lead to the retention and acquisition of power. Status, related to the respect one has in the eyes of others, generates expectations for behavior and opportunities for advancement that favor those with a prior status advantage. We also explore the role that hierarchy-enhancing belief systems play in stabilizing hierarchy, both from the bottom up and from the top down. Finally, we address a number of factors that we think are instrumental in explaining the conditions under which hierarchies change. Our framework suggests a number of avenues for future research on the bases, causes, and consequences of hierarchy in groups and organizations.