We examine how entrepreneurs shape organizational boundaries and construct markets through an inductive, longitudinal study of five ventures. Our central contribution is a framework of how successful entrepreneurs attempt to dominate nascent markets by co-constructing organizational boundaries and market niches using three processes: claiming, demarcating, and controlling a market. We propose that power is the underlying boundary logic and indicate the "soft-power" strategies by which entrepreneurs compete in highly ambiguous markets. Overall, we develop a holistic view of organizational boundaries and offer insights into institutional entrepreneurship and resource dependence theories. Our most important contribution is reinvigorating the study of interorganizational power.