Entrepreneurial legitimacy scholars have established legitimacy as “the most pressing issue” facing early-stage entrepreneurs (Lounsbury & Glynn, 2001: 550) and studied strategies by which founders can develop impressions of themselves and their businesses as being desirable and appropriate in front of audiences ranging from peers and investors to government agencies, to corporate gatekeepers, to early adopters. In this essay, we introduce the entrepreneur themself as an important audience making legitimacy judgments and specify how extant theorizing suggests evaluations of self-legitimacy are linked to entrepreneurial behavior. Adopting a social cognitive approach (Bandura, 1986), we define and develop a dynamic framework for entrepreneurial self-legitimacy (ESL) wherein, over time, individuals experience various states along a spectrum that integrates the independently developed concepts of impostor phenomenon at one extreme and hubris at the other. We illustrate the mindsets and behavioral tendencies that result from low and high ESL, emphasizing that both ends of the spectrum have ‘bright’ and ‘dark’ sides. In consolidating rich constructs into a common framework, our work contributes an important new perspective to conversations on entrepreneurial legitimacy and entrepreneurial social cognition. We finish by outlining avenues for future research on ESL, including the capacity of such work to practically support the trajectories of entrepreneurs.